Today there are in arxiv two articles that look really great.
The firs (in the order that arxiv gives to them) is from Samir D. Mathur: Effective information loss outside the horizon.
It argues that there is no loss of information inside a black hole because he information simply doesn't go inside the black hole. The abstract explains it more carefully:
If a system falls through a black hole horizon, then its information is lost to an observer at infinity. But we argue that the {\it accessible} information is lost {\it before} the horizon is crossed. The temperature of the hole limits information carrying signals from a system that has fallen too close to the horizon. Extremal holes have T=0, but there is a minimum energy required to emit a quantum in the short proper time left before the horizon is crossed. If we attempt to bring the system back to infinity for observation, then acceleration radiation destroys the information. All three considerations give a critical distance from the horizon $d\sim \sqrt{r_H\over \Delta E}$, where $r_H$ is the horizon radius and $\Delta E$ is the energy scale characterizing the system. For systems in string theory where we pack information as densely as possible, this acceleration constraint is found to have a geometric interpretation. These estimates suggest that in theories of gravity we should measure information not as a quantity contained inside a given system, but in terms of how much of that information can be reliably accessed by another observer.
The other article is written by Maldacena: Einstein Gravity from Conformal Gravity.
The abstract is:
We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the ghosts of conformal gravity from this computation. In the case of a five dimensional pure gravity theory with a positive cosmological constant we show that the late time superhorizon tree level probability measure, $|\Psi [ g ]|^2$, for its four dimensional spatial slices is given by the action of Euclidean four dimensional conformal gravity.">We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the ghosts of conformal gravity from this computation.
In the case of a five dimensional pure gravity theory with a positive cosmological constant we show that the late time superhorizon tree level probability measure, $|\Psi [ g ]|^2$, for its four dimensional spatial slices is given by the action of Euclidean four dimensional conformal gravity.
Unfortunately until the next Friday I am going to be very busy and I badly will have time to read them carefully those days so I can't say too much more about them. I suppose that (at least) Lubos will talk about them so I will read its report before I can read them myself. I write this entry partially to recommend the articles to however could be interested and also to keep a link to them so I could later have a quick access to them from wherever I want.
Update: Well, at last I had no patient and read the first article (after all is a brief one, only 7 pages). I have a mixed filling about it. The author computes a few things related to the fall of a body towards an event horizon. Firstly he does for an Schwarschild one.
There he considers two cases. The first in the free fall. In that case the last light (containing the info about the object) is emitted, because of the red-shift at a frequency bellow the Hawking temperature and so it can't be differentiated from this and he concludes that we actually don't have the information about that object.
The second case is when an observer at infinity holds the infalling object until the last time. In that case it is the unrhu radiation associated to the acceleration of an object at rest respect to a gravitational field which is responsible for a dissipation of the information of the object when it finally is released and cross the horizont.
Later he calculates similar things for a Reissner-Nordstöm like black hole and he finds that somewhat different mechanism operate in order to get similar qualitative and quantitative results.
In the last part he does calculations using string theory and the fuzzball paradigm for black holes (where the notion of event horizon is replaced by an stringy construction). Still he finds equivalent results.
Certainly the fact that many different calculations lead to a similar result is appealing. But still I don't see clear the whole subject. I think that at best he would be saying that the lost of information happens before the horizon (or its fuzzball "equivalent") so the problem of lost of unitarity remains (and even we could say that is getting worst because it happens in a region causally connected with the outsider observer). But the whole thing is that one could think that a priory we could think that if the outside of the black hole is clean of other infalling matter (other that the actual object under study) we could argue that if we know the state of the object at infinity we can apply the laws of quantum mechanics to know t's state when it is falling (eve it we can't actually do a measure to be sure that nothing has perturbed our object). That contrast the case of the object that falls behind the horizon when we have no idea of which it's final state would be because we don't know the laws of quantum gravity near the singularity. Well, I am ware that this last objection is somewhat wrong because the key point of the lost of information is the horizon and not the singularity but I have no more time just now to see what point I am missing. I'll realize it for sure later, but I don't promise to write it here soon. But keep calm, for sure Lubos will write about it sooner or later and will clarify the relevant points ;).
Monday, May 30, 2011
Tuesday, April 19, 2011
Can we see inside black holes?
The last week there was an article that was commented in the arxiv blog: Planets Could Orbit Singularities Inside Black Holes.
The blog entry discuses this article: Is there life inside black holes?.
The article is a pure classical relativity article. It study the possibility of stable orbits for planets inside a black hole, in particular in a Kerr-Newman black hole, that is, a rotting charged black hole. The classical geometry of a Kerr-Newman black hole is described by it's Penrose diagram:
The essential aspect of the K-N black holes for the work of that people is the presence of the inner horizon (a Cauchy horizon). In a non rotating black hole, described by the Schwarschild metric, once he cross the event horizon the radial coordinate changes it sign acquiring a time sign. That means that one must go in the direction of decreasing radius until one finds the central point-like singularity. A common interpretation of that geometry is to say that inside the black hole the space itself is falling toward the centre at the speed of light and it drags averything with it.
In the K-N case things are somewhat richer. In addition to the outer event horizon there is an inner cauchy horizon. When the black holes spins faster and faster (or when the charge of the black hole increases) both horizons get nearest and nearest until, ultimately, they would converge and it would become an extreme black hole.Beyond that one would have a naked singularity but it is thought that such a possibility should be ruled out.
well, as a I said te key point was the cuchy horizon. AS you can read in the linked wikipedia article a Cauchy Horizon is a boundary for the validity of a well posed Cauchy problem in partial differential equations. It can be shown that light (or whatever wave) crossing the horizon gets an infinite blue-shift. That means that it's energy-momentum tensor diverges. The implication of it would be that the back-reaction would destroy the Cauchy horizon once a particle cross it. Still one could get an stable Cauchy horizon if one throws in it exotic matter violating the AWEC (average weak energy condition) well known for people working in wormholes.
The reason why the cauchy horizon is important is because once it is crossed the radial coordinate becomes once again space like. That opens the possibility of the existence of stable orbits inside the black hole. In previous articles, cited by the author, it was shown the existence of that orbits for Reisner-Nordstöm (charged) and Kerr (rotating) black holes. The present article generalizes the results to the general case. In the article considerations are hold about the tidal forces, sizes, radiation rates and they conclude that in a galaxy centre sized black hole a planet could do an stable orbit around the singularity and hold life.
Well, this is the content of the article. As I have explained it is worked in the ansatz of the validity of classical relativity inside a black hole. Also it depends strongly in the stability of the cauchy horizon that can't be got without exotic matter. Note: the author doesn't mention that point about exotic matter although he is aware of the fact that cauchy horizons are not stable. Without exotic matter the whole paper is of a purely academic interest even if one accepts that classical general relativity is accurate to describe black holes inners.
Of course there are a lot of people who don't like classical GR for doing so. In string theory there are many alternative descriptions. On one side one has the correspondence principle of black holes (due to t' hooft and Suskind) that says that an observer falling into a black hole will not be able to notice when he has crossed the even horizon. That means that the physic he sees is must be equal that the physics seen by an outside observer. The reason of the introduction of that principle is the intent of saving unitarity in the presence of Hawking radiation. The actual reasoning is made not classically but for the Hilbert space of a quantum theory as seen but inner and outer observers.
Another string theory inspired viewpoint is described in a classical article by Maldacena: D-brane Approach to Black Hole Quantum Mechanics . In the last part of that article, after calculating the Beckenstein-Hawking entropy, Maldacena Suggest a view where black holes inners and Hawking radiation is described in terms of D-branes. I am not aware if that suggestion has been further developed. I have made a partial search for "hawking radiation in string theory" but I haven't found too much. In fact, beyond that Maldacena article, I found only an approach written some years before using a very aproximative description.
Another paradigm for black hole inners in the string literature would be the fuzzball approach of Mahupart (or maybe Mithur I am not sure at this point and have not time to do a search just now).
Well, that variety of viewpoints, not very compatible among them, for the black hole inner is disappointing. Even in the simpler case of the general relativity viewpoint is disappointing the possibility of the existence of stable structures (maybe planets of an advanced alien civilization, maybe a much more prosaic rings of dust) existing inside the black hole hidden for us from the event horizon.
But, wait! The title of the post wonders about the possibility of seeing inside the black hole. Of course classically it is impossible because of the very meaning of "event horizon". But when quantum mechanics enter the game thing could change. Of course the key would be Hawking radiation. The semiclassical theory says that the radiation must be purely thermodynamic so we can't get any info from it. But if unitarity is conserved the Hawking radiation can't be purely thermodynamic and it must have some structure that stores all the structure of the matter that formed the black hole and that has fallen inside it after it's formation. Possibly it will also have some information about the inner structure of the black hole. Obviously to get that info is very difficult in practice. The usual analogy is to say that one could reconstruct, in principle, the form of a living object from the ashes that are produced when it is burn.
But if we are a little least ambitious maybe we could actually get some partial information. Maybe we could design some easy mental experiment in which throwing into the black hole some specific kind of matter in some specific way we could analyse the Hawking radiation related to it to get some information of the inside of the horizon. That would actually be very cool because it would give an experimental way to distinguish the competing descriptions of the black hole inner.
Of course I actually don't know the details of how this could be done (only a very vague ideas that probably will not work). But maybe something on this purpose is already made and a kind reader would give me the references ;).
The blog entry discuses this article: Is there life inside black holes?.
The article is a pure classical relativity article. It study the possibility of stable orbits for planets inside a black hole, in particular in a Kerr-Newman black hole, that is, a rotting charged black hole. The classical geometry of a Kerr-Newman black hole is described by it's Penrose diagram:
The essential aspect of the K-N black holes for the work of that people is the presence of the inner horizon (a Cauchy horizon). In a non rotating black hole, described by the Schwarschild metric, once he cross the event horizon the radial coordinate changes it sign acquiring a time sign. That means that one must go in the direction of decreasing radius until one finds the central point-like singularity. A common interpretation of that geometry is to say that inside the black hole the space itself is falling toward the centre at the speed of light and it drags averything with it.
In the K-N case things are somewhat richer. In addition to the outer event horizon there is an inner cauchy horizon. When the black holes spins faster and faster (or when the charge of the black hole increases) both horizons get nearest and nearest until, ultimately, they would converge and it would become an extreme black hole.Beyond that one would have a naked singularity but it is thought that such a possibility should be ruled out.
well, as a I said te key point was the cuchy horizon. AS you can read in the linked wikipedia article a Cauchy Horizon is a boundary for the validity of a well posed Cauchy problem in partial differential equations. It can be shown that light (or whatever wave) crossing the horizon gets an infinite blue-shift. That means that it's energy-momentum tensor diverges. The implication of it would be that the back-reaction would destroy the Cauchy horizon once a particle cross it. Still one could get an stable Cauchy horizon if one throws in it exotic matter violating the AWEC (average weak energy condition) well known for people working in wormholes.
The reason why the cauchy horizon is important is because once it is crossed the radial coordinate becomes once again space like. That opens the possibility of the existence of stable orbits inside the black hole. In previous articles, cited by the author, it was shown the existence of that orbits for Reisner-Nordstöm (charged) and Kerr (rotating) black holes. The present article generalizes the results to the general case. In the article considerations are hold about the tidal forces, sizes, radiation rates and they conclude that in a galaxy centre sized black hole a planet could do an stable orbit around the singularity and hold life.
Well, this is the content of the article. As I have explained it is worked in the ansatz of the validity of classical relativity inside a black hole. Also it depends strongly in the stability of the cauchy horizon that can't be got without exotic matter. Note: the author doesn't mention that point about exotic matter although he is aware of the fact that cauchy horizons are not stable. Without exotic matter the whole paper is of a purely academic interest even if one accepts that classical general relativity is accurate to describe black holes inners.
Of course there are a lot of people who don't like classical GR for doing so. In string theory there are many alternative descriptions. On one side one has the correspondence principle of black holes (due to t' hooft and Suskind) that says that an observer falling into a black hole will not be able to notice when he has crossed the even horizon. That means that the physic he sees is must be equal that the physics seen by an outside observer. The reason of the introduction of that principle is the intent of saving unitarity in the presence of Hawking radiation. The actual reasoning is made not classically but for the Hilbert space of a quantum theory as seen but inner and outer observers.
Another string theory inspired viewpoint is described in a classical article by Maldacena: D-brane Approach to Black Hole Quantum Mechanics . In the last part of that article, after calculating the Beckenstein-Hawking entropy, Maldacena Suggest a view where black holes inners and Hawking radiation is described in terms of D-branes. I am not aware if that suggestion has been further developed. I have made a partial search for "hawking radiation in string theory" but I haven't found too much. In fact, beyond that Maldacena article, I found only an approach written some years before using a very aproximative description.
Another paradigm for black hole inners in the string literature would be the fuzzball approach of Mahupart (or maybe Mithur I am not sure at this point and have not time to do a search just now).
Well, that variety of viewpoints, not very compatible among them, for the black hole inner is disappointing. Even in the simpler case of the general relativity viewpoint is disappointing the possibility of the existence of stable structures (maybe planets of an advanced alien civilization, maybe a much more prosaic rings of dust) existing inside the black hole hidden for us from the event horizon.
But, wait! The title of the post wonders about the possibility of seeing inside the black hole. Of course classically it is impossible because of the very meaning of "event horizon". But when quantum mechanics enter the game thing could change. Of course the key would be Hawking radiation. The semiclassical theory says that the radiation must be purely thermodynamic so we can't get any info from it. But if unitarity is conserved the Hawking radiation can't be purely thermodynamic and it must have some structure that stores all the structure of the matter that formed the black hole and that has fallen inside it after it's formation. Possibly it will also have some information about the inner structure of the black hole. Obviously to get that info is very difficult in practice. The usual analogy is to say that one could reconstruct, in principle, the form of a living object from the ashes that are produced when it is burn.
But if we are a little least ambitious maybe we could actually get some partial information. Maybe we could design some easy mental experiment in which throwing into the black hole some specific kind of matter in some specific way we could analyse the Hawking radiation related to it to get some information of the inside of the horizon. That would actually be very cool because it would give an experimental way to distinguish the competing descriptions of the black hole inner.
Of course I actually don't know the details of how this could be done (only a very vague ideas that probably will not work). But maybe something on this purpose is already made and a kind reader would give me the references ;).
Thursday, February 17, 2011
String theory in exotic R^4
Today in arxiv there is a very curious article:Quantum D-branes and exotic smooth R^4 written by Torsten Asselmeyer-Maluga, Jerzy Krol.
The article is actually the second part of a previous one: Exotic smooth R^4 and certain configurations of NS and D branes in string theory.
The abstract of the first (in date order) article reads:
In this paper we show that in some important cases 4-dimensional data can be extracted from superstring theory such that a) the data are 4 Euclidean geometries embedded in standard $\mathbb{R}^{4}$, b) these data depend on NS and D brane charges of some string backgrounds, c) it is of potential relevance to 4-dimensional physics, d) the compactification and stabilization techniques are not in use, but rather are replaced. We analyze certain configurations of NS and D-branes in the context of $SU(2)$ WZW model and find the correlations with different exotic smoothings of $\mathbb{R}^{4}$. First, the dynamics of D-branes in $SU(2)$ WZW model at finite $k$, i.e. the charges of the branes, refers to the exoticness of ambient $\mathbb{R}^{4}$. Next, the correspondence between exotic smoothness on 4-space, transversal to the world volume of NS5 branes in IIA type, and the number of these NS5 branes follows. Finally, the translation of 10 dimensional string backgrounds to 4 Euclidean spaces embedded as open subsets in the standard $\mathbb{R}^{4}$ is achieved.
I still haven't had time to read the full article, but it looks quite interesting, and beautifully, specially from the perspective of someone whose favourite area of maths is topology. The idea is to see if someone can make string theory in a background of R^4 with a different differential structure than the usual one. One of the most amazing discoveries of differential topology was that there were different differential structures for R^4 than the usual one. That means that although like a topological manifold R^4 is unique there are different differentiable manifolds that are compatible with it's topological structure. An explicit characterization of that exotic structures in terms of coordinate is difficult and their existence is proved by means of topological techniques. In the paper it is made use of h-cobordism.
Later he begins the string theoretical construction, using SU(2) WZW (wess-zumino-witten= CFT's, NS 5 branes, D branes, etc. AS I still haven't read the article carefully, nor the continuation of it (the today's arxiv article ) wouldn't give more details. Only to say that it looks like a very intriguing area of research.
Also today in arxiv there is a very interesting, but much more conventional article of Miche Dine: Supersymmetry from the Top Down whose abstract is:
If supersymmetry turns out to be a symmetry of nature at low energies, the first order of business to measure the soft breaking parameters. But one will also want to understand the symmetry, and its breaking, more microscopically. Two aspects of this problem constitute the focus of these lectures. First, what sorts of dynamics might account for supersymmetry breaking, and its manifestation at low energies. Second, how might these features fit into string theory (or whatever might be the underlying theory in the ultraviolet). The last few years have seen a much improved understanding of the first set of questions, and at least a possible pathway to address the second.">If supersymmetry turns out to be a symmetry of nature at low energies, the first order of business to measure the soft breaking parameters. But one will also want to understand the symmetry, and its breaking, more microscopically. Two aspects of this problem constitute the focus of these lectures. First, what sorts of dynamics might account for supersymmetry breaking, and its manifestation at low energies. Second, how might these features fit into string theory (or whatever might be the underlying theory in the ultraviolet). The last few years have seen a much improved understanding of the first set of questions, and at least a possible pathway to address the second.
The article is quite pedagogical, and even begins with an ultra fast introduction to supersymmetry. Certainly recommendable.
On the subject of supersymmetry in the LHC era I thing that everybody would must read the last entry of Jester's blog: What LHC tells about SUSY that discussed the paper of the ATLAS collaboration: Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in sqrt{s} = 7 TeV pp.
Well, certainly the expectations of Lubos of an early discovery of SUSY in the LHC are gone, but still there are good reasons to be patient, as explained by Lubos himself or by the Dine's paper.
By the way, while writing this entry I have seen that Lubos himself has written an entry about the Dines paper, you can read it here. At the moment of writing my entry he hasn't given many details about the article, but possibly he will edit his post and discuss the paper in more detail.
Update: Lubos has read this entry and has written a very intersting essay about the general relevance (or irrelevance) of the pathological mathematical structures in physics .
About the actual series of papers in exotic R^4 he doesn't say too much because he claims that he doesn't understand the paper. I have been studying the subject, including some references, and I am still going on. Much of the mathematics (differential topology: h-cobordism, topological surgery, tubular neighbourhoods) are familiar to me, but some more recent concepts are new to me. Still I think that I can follow the general argumentative line of the mat part. I get somewhat more loose in other points of the WZW model in an SU(2) background, but still I think that I get the general argumentation. As soon as I end reading a few more references I'll try to expose the key ideas.
Anyway, there is a difference here with the case commented but Lubos. R^4 is the only R^n that admits different smooth structures for the same topological structure. In that aspect it is not a case of searching for a pathology but a case where the pathology appears by itself. In fact most people who have heard about that particularity of R^4 have always though that maybe that could be the ultimate reason that we live in a four dimensional manifold. Of course what they lacked is a way to relate that peculiarity of R^4 to any actual physic. This people seem to have advanced somewhat in that direction, but as far as I understood they are far of the objective (if that is their objective, that probably it is not the case).
The article is actually the second part of a previous one: Exotic smooth R^4 and certain configurations of NS and D branes in string theory.
The abstract of the first (in date order) article reads:
In this paper we show that in some important cases 4-dimensional data can be extracted from superstring theory such that a) the data are 4 Euclidean geometries embedded in standard $\mathbb{R}^{4}$, b) these data depend on NS and D brane charges of some string backgrounds, c) it is of potential relevance to 4-dimensional physics, d) the compactification and stabilization techniques are not in use, but rather are replaced. We analyze certain configurations of NS and D-branes in the context of $SU(2)$ WZW model and find the correlations with different exotic smoothings of $\mathbb{R}^{4}$. First, the dynamics of D-branes in $SU(2)$ WZW model at finite $k$, i.e. the charges of the branes, refers to the exoticness of ambient $\mathbb{R}^{4}$. Next, the correspondence between exotic smoothness on 4-space, transversal to the world volume of NS5 branes in IIA type, and the number of these NS5 branes follows. Finally, the translation of 10 dimensional string backgrounds to 4 Euclidean spaces embedded as open subsets in the standard $\mathbb{R}^{4}$ is achieved.
I still haven't had time to read the full article, but it looks quite interesting, and beautifully, specially from the perspective of someone whose favourite area of maths is topology. The idea is to see if someone can make string theory in a background of R^4 with a different differential structure than the usual one. One of the most amazing discoveries of differential topology was that there were different differential structures for R^4 than the usual one. That means that although like a topological manifold R^4 is unique there are different differentiable manifolds that are compatible with it's topological structure. An explicit characterization of that exotic structures in terms of coordinate is difficult and their existence is proved by means of topological techniques. In the paper it is made use of h-cobordism.
Later he begins the string theoretical construction, using SU(2) WZW (wess-zumino-witten= CFT's, NS 5 branes, D branes, etc. AS I still haven't read the article carefully, nor the continuation of it (the today's arxiv article ) wouldn't give more details. Only to say that it looks like a very intriguing area of research.
Also today in arxiv there is a very interesting, but much more conventional article of Miche Dine: Supersymmetry from the Top Down whose abstract is:
If supersymmetry turns out to be a symmetry of nature at low energies, the first order of business to measure the soft breaking parameters. But one will also want to understand the symmetry, and its breaking, more microscopically. Two aspects of this problem constitute the focus of these lectures. First, what sorts of dynamics might account for supersymmetry breaking, and its manifestation at low energies. Second, how might these features fit into string theory (or whatever might be the underlying theory in the ultraviolet). The last few years have seen a much improved understanding of the first set of questions, and at least a possible pathway to address the second.">If supersymmetry turns out to be a symmetry of nature at low energies, the first order of business to measure the soft breaking parameters. But one will also want to understand the symmetry, and its breaking, more microscopically. Two aspects of this problem constitute the focus of these lectures. First, what sorts of dynamics might account for supersymmetry breaking, and its manifestation at low energies. Second, how might these features fit into string theory (or whatever might be the underlying theory in the ultraviolet). The last few years have seen a much improved understanding of the first set of questions, and at least a possible pathway to address the second.
The article is quite pedagogical, and even begins with an ultra fast introduction to supersymmetry. Certainly recommendable.
On the subject of supersymmetry in the LHC era I thing that everybody would must read the last entry of Jester's blog: What LHC tells about SUSY that discussed the paper of the ATLAS collaboration: Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in sqrt{s} = 7 TeV pp.
Well, certainly the expectations of Lubos of an early discovery of SUSY in the LHC are gone, but still there are good reasons to be patient, as explained by Lubos himself or by the Dine's paper.
By the way, while writing this entry I have seen that Lubos himself has written an entry about the Dines paper, you can read it here. At the moment of writing my entry he hasn't given many details about the article, but possibly he will edit his post and discuss the paper in more detail.
Update: Lubos has read this entry and has written a very intersting essay about the general relevance (or irrelevance) of the pathological mathematical structures in physics .
About the actual series of papers in exotic R^4 he doesn't say too much because he claims that he doesn't understand the paper. I have been studying the subject, including some references, and I am still going on. Much of the mathematics (differential topology: h-cobordism, topological surgery, tubular neighbourhoods) are familiar to me, but some more recent concepts are new to me. Still I think that I can follow the general argumentative line of the mat part. I get somewhat more loose in other points of the WZW model in an SU(2) background, but still I think that I get the general argumentation. As soon as I end reading a few more references I'll try to expose the key ideas.
Anyway, there is a difference here with the case commented but Lubos. R^4 is the only R^n that admits different smooth structures for the same topological structure. In that aspect it is not a case of searching for a pathology but a case where the pathology appears by itself. In fact most people who have heard about that particularity of R^4 have always though that maybe that could be the ultimate reason that we live in a four dimensional manifold. Of course what they lacked is a way to relate that peculiarity of R^4 to any actual physic. This people seem to have advanced somewhat in that direction, but as far as I understood they are far of the objective (if that is their objective, that probably it is not the case).
Friday, February 11, 2011
String theory and nanotechnology meet today in arxiv
String theory deal mainly with physic at the planck scale, although it's goal is to connect to with the electroweak scale.
On the other hand, nonotehcnology, deals with physics at sizes similar to the Bohr radius. There are, consequently, many orders of magnitude of difference among that two branches of physics.
Because of that it is absolutely amazing to see in the title of the paper a reference to a relation among them. But today in arxiv we have such a paper: Fermionic condensate and Casimir densities in the presence of compact dimensions with applications to nanotubes.
The abstract reads like this:
We investigate the fermionic condensate and the vacuum expectation value of the energy-momentum tensor for a massive fermionic field in the geometry of two parallel plate on the background of Minkowski spacetime with an arbitrary number of toroidally compactified spatial dimensions, in the presence of a constant gauge field. Bag boundary conditions are imposed on the plates and periodicity conditions with arbitrary phases are considered along the compact dimensions. The boundary induced parts in the fermionic condensate and the vacuum energy density are negative, with independence of the phases in the periodicity conditions and of the value of the gauge potential. Interaction forces between the plates are thus always attractive. However, in physical situations where the quantum field is confined to the region between the plates, the pure topological part contributes as well, and then the resulting force can be either attractive or repulsive, depending on the specific phases encoded in the periodicity conditions along the compact dimensions, and on the gauge potential, too. Applications of the general formulas to cylindrical carbon nanotubes are considered, within the framework of a Dirac-like theory for the electronic states in graphene. In the absence of a magnetic flux, the energy density for semiconducting nanotubes is always negative. For metallic nanotubes the energy density is positive for long tubes and negative for short ones. The resulting Casimir forces acting on the edges of the nanotube are attractive for short tubes with independence of the tube chirality. The sign of the force for long nanotubes can be controlled by tuning the magnetic flux. This opens the way to the design of efficient actuators driven by the Casimir force at the nanoscale.
I haven't read in deep the paper, but in a superficial reading I have got a confirmation that they are actually claiming that actual aspects of the compactified extra dimensions of string theory could, through the Casimir effect observable consequences in the characteristics of nanotechnologic materials, in particular nanotubes. My guess is that there must be some error, or some trick, somewhere. If not this paper would be driving string theory from the realms of cute edge speculative high energy physics to actual applications in one of the most economicaly profitable industries. Too good to be truth probably, but, who knows? Well, I'll read the article carefully sooner and I'll comment more details. But I doubt that I would be the only one to say something about it ;)-
Update: Ok, the article actually doesn't relate string theory extra dimensions and carbone nanotubes. IT only applies the formalism of compactificactions to nanotubes, based on the premise that a nanotube is a cylinder, i.e. a compactified plane. The introductions, and many other parts of the article are somewhat misleading and seem to suggest what I had explained. Also it is misleading the fact that it appears inhep-th. The reason for that possibly is that they make some development of the formalism of compactifications in a general, multidimensional, framework. Possibly that general development could be usefull for people working in string theory, that possibly justifies the inclussion of the paper in hep-th although the primal subjecto of the paper is condensed matter physic.
On the other hand, nonotehcnology, deals with physics at sizes similar to the Bohr radius. There are, consequently, many orders of magnitude of difference among that two branches of physics.
Because of that it is absolutely amazing to see in the title of the paper a reference to a relation among them. But today in arxiv we have such a paper: Fermionic condensate and Casimir densities in the presence of compact dimensions with applications to nanotubes.
The abstract reads like this:
We investigate the fermionic condensate and the vacuum expectation value of the energy-momentum tensor for a massive fermionic field in the geometry of two parallel plate on the background of Minkowski spacetime with an arbitrary number of toroidally compactified spatial dimensions, in the presence of a constant gauge field. Bag boundary conditions are imposed on the plates and periodicity conditions with arbitrary phases are considered along the compact dimensions. The boundary induced parts in the fermionic condensate and the vacuum energy density are negative, with independence of the phases in the periodicity conditions and of the value of the gauge potential. Interaction forces between the plates are thus always attractive. However, in physical situations where the quantum field is confined to the region between the plates, the pure topological part contributes as well, and then the resulting force can be either attractive or repulsive, depending on the specific phases encoded in the periodicity conditions along the compact dimensions, and on the gauge potential, too. Applications of the general formulas to cylindrical carbon nanotubes are considered, within the framework of a Dirac-like theory for the electronic states in graphene. In the absence of a magnetic flux, the energy density for semiconducting nanotubes is always negative. For metallic nanotubes the energy density is positive for long tubes and negative for short ones. The resulting Casimir forces acting on the edges of the nanotube are attractive for short tubes with independence of the tube chirality. The sign of the force for long nanotubes can be controlled by tuning the magnetic flux. This opens the way to the design of efficient actuators driven by the Casimir force at the nanoscale.
I haven't read in deep the paper, but in a superficial reading I have got a confirmation that they are actually claiming that actual aspects of the compactified extra dimensions of string theory could, through the Casimir effect observable consequences in the characteristics of nanotechnologic materials, in particular nanotubes. My guess is that there must be some error, or some trick, somewhere. If not this paper would be driving string theory from the realms of cute edge speculative high energy physics to actual applications in one of the most economicaly profitable industries. Too good to be truth probably, but, who knows? Well, I'll read the article carefully sooner and I'll comment more details. But I doubt that I would be the only one to say something about it ;)-
Update: Ok, the article actually doesn't relate string theory extra dimensions and carbone nanotubes. IT only applies the formalism of compactificactions to nanotubes, based on the premise that a nanotube is a cylinder, i.e. a compactified plane. The introductions, and many other parts of the article are somewhat misleading and seem to suggest what I had explained. Also it is misleading the fact that it appears inhep-th. The reason for that possibly is that they make some development of the formalism of compactifications in a general, multidimensional, framework. Possibly that general development could be usefull for people working in string theory, that possibly justifies the inclussion of the paper in hep-th although the primal subjecto of the paper is condensed matter physic.
Thursday, January 27, 2011
Two cosmology papes and the question of extra dimensions
First an advert, the two topics are unrelated, well, or may be not ;).
The first paper I would want to mention is this form Luis Alvarez Gaumé. Gaumé is one of the best known spanish string theorists. He is famous for the 80's paper with Witten about the (absence of) anomalies in string theory.
Now he has a paper in arxiv. A Minimal Inflation Scenario. This is the abstract:
We elaborate on a minimal inflation scenario based entirely on the general properties of supersymmetry breaking in supergravity models. We identify the inflaton as the scalar component of the Goldstino superfield. We write plausible candidates for the effective action describing this chiral superfield. In particular the theory depends (apart from parameters of O(1)) on a single free parameter: the scale of supersymmetry breaking. This can be fixed using the amplitude of CMB cosmological perturbations and we therefore obtain the scale of supersymmetry breaking to be 10^{12-14} GeV. The model also incorporates explicit R-symmetry breaking in order to satisfy the slow roll conditions. In our model the eta-problem is solved without extra fine-tuning. We try to obtain as much information as possible in a model independent way using general symmetry properties of the theory's effective action, this leads to a new proposal on how to exit the inflationary phase and reheat the Universe.
I am far from expert in the inflation technicalities but it looks like a quite natural proposal (well, maybe except for explicit R-parity breaking, which, otherwise, is good for some very specific models of dark matter tht were popular the last year trying to accommodate some now not too much discussed anomalies from PAMELA, ARTIC and others).
The other cosmology paper I wanted to mention is this: Holographic unification of dark matter and dark energy. The abstract is as follows: Using a new version of the holographic principle, a constant term was introduced, which conduces to the description of the standard cosmological LCDM model, and unifies under the same concept the dark matter and dark energy phenomena. The obtained model improves the results of previously considered holographic models based on local quantities. The inclusion of constant term is interpreted as a natural first approximation for the infrared cutoff which is associated with the vacuum energy, and the additional terms guarantee an appropriate evolutionary scenario that fits the astrophysical observations. The model allows to reproduce the standard LCDM model without explicitly introducing matter content, and using only geometrical quantities. It is also obtained that the model may describe the dark energy beyond the standard LCDM.
The idea of unifying dark matter and dark energy as one and the same phenomena looks interesting aesthetically. Against it it is the question of many independent observations leading to the existence of dark matter. Specially he galactic ones seem a little bit out of the sight of this paper. But I remember a paper a few time ago that could fit the rotation of galaxies by mean of an stringy phenomena without need of dark matter. Still there is a good reason for expecting the existence of dark matter: Supersymmetry. Specially if R-parity is conserved the LSP is stable and would be a component of dark matter. And one expect that supersymmetry would break near the electroweak scale, isn't it?
Well, maybe. But one of the main supports of low energy SSB is the resolution of the hierarchy problem. Fortunately there is another option for solving the hierarchy problem, the Randall-Sumdrum scenaries. Recently there were two results from the tevatron announcing two anomalies at more than 3 sigmas related to top quark physics. One is described in the article: Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production., Annalized in entries in the Lubos and Jester blog, among others.
The other, more recent one, was first announced in the Jester's blog: Another Intriguing Result from Tevatron's CDF that also was analysed in Lubos blog (I don' put the link because everybody reads Lubos blog, isn't it? ;) ).
Reading the entries, and the comments one sees that there is a main natural candidate for both phenomena, a KK (kaluza-klein) partner of the gluon. For that KK gluon being in the right track one must be in a Randall-Sumdrum scenario. That means that if the LHC, that restart it's operation in fabruary, confirms the anomalies we would have a (very likely) confirmation of the existence of extra dimensions which would be possibly the most amazing all times experimental discovery in physics.
But don't shout Eureka still. Recently the LHC published an article advertising that they had not seen evidence of micro black holes, which is a bad thing for the R-S sceneries. Well, one wouldn't care too much about it. Microscopic B-h are not the former prediction of R-S scenaries and the paper had some drawbacks also.
Yesterday there was a paper about this R-S braneworlds proposal and it's measure in the LHC: LHC bounds on large extra dimensions based on the analysis of 3.1 inverse picobarns of LHC data that fixed new limits in the possible extent of the extra dimensions. AS far as I understand that bounds don't forbid the KK gluon as the author of the top quarks anomalies. Of course there are another possible answers to that anomalies. For example Marco Frasca claims (The Tevatron affair and the “fat” gluon )that his model of "fat gluon" could do the job (although he acknowledges that the KK gluon fits better).
Well, the thing is that if braneworlds are proved valid the motivation for weak scale SSB would be lacking (because R-S would solve the hierarchy problem), and with it the best candidates for dark matter. Still one could think that another KK particle are candidates for dark matter. But maybe the theories that unifies dark matter and dark energy would gain some points, or maybe be not, cosmology you know ;).
The first paper I would want to mention is this form Luis Alvarez Gaumé. Gaumé is one of the best known spanish string theorists. He is famous for the 80's paper with Witten about the (absence of) anomalies in string theory.
Now he has a paper in arxiv. A Minimal Inflation Scenario. This is the abstract:
We elaborate on a minimal inflation scenario based entirely on the general properties of supersymmetry breaking in supergravity models. We identify the inflaton as the scalar component of the Goldstino superfield. We write plausible candidates for the effective action describing this chiral superfield. In particular the theory depends (apart from parameters of O(1)) on a single free parameter: the scale of supersymmetry breaking. This can be fixed using the amplitude of CMB cosmological perturbations and we therefore obtain the scale of supersymmetry breaking to be 10^{12-14} GeV. The model also incorporates explicit R-symmetry breaking in order to satisfy the slow roll conditions. In our model the eta-problem is solved without extra fine-tuning. We try to obtain as much information as possible in a model independent way using general symmetry properties of the theory's effective action, this leads to a new proposal on how to exit the inflationary phase and reheat the Universe.
I am far from expert in the inflation technicalities but it looks like a quite natural proposal (well, maybe except for explicit R-parity breaking, which, otherwise, is good for some very specific models of dark matter tht were popular the last year trying to accommodate some now not too much discussed anomalies from PAMELA, ARTIC and others).
The other cosmology paper I wanted to mention is this: Holographic unification of dark matter and dark energy. The abstract is as follows: Using a new version of the holographic principle, a constant term was introduced, which conduces to the description of the standard cosmological LCDM model, and unifies under the same concept the dark matter and dark energy phenomena. The obtained model improves the results of previously considered holographic models based on local quantities. The inclusion of constant term is interpreted as a natural first approximation for the infrared cutoff which is associated with the vacuum energy, and the additional terms guarantee an appropriate evolutionary scenario that fits the astrophysical observations. The model allows to reproduce the standard LCDM model without explicitly introducing matter content, and using only geometrical quantities. It is also obtained that the model may describe the dark energy beyond the standard LCDM.
The idea of unifying dark matter and dark energy as one and the same phenomena looks interesting aesthetically. Against it it is the question of many independent observations leading to the existence of dark matter. Specially he galactic ones seem a little bit out of the sight of this paper. But I remember a paper a few time ago that could fit the rotation of galaxies by mean of an stringy phenomena without need of dark matter. Still there is a good reason for expecting the existence of dark matter: Supersymmetry. Specially if R-parity is conserved the LSP is stable and would be a component of dark matter. And one expect that supersymmetry would break near the electroweak scale, isn't it?
Well, maybe. But one of the main supports of low energy SSB is the resolution of the hierarchy problem. Fortunately there is another option for solving the hierarchy problem, the Randall-Sumdrum scenaries. Recently there were two results from the tevatron announcing two anomalies at more than 3 sigmas related to top quark physics. One is described in the article: Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production., Annalized in entries in the Lubos and Jester blog, among others.
The other, more recent one, was first announced in the Jester's blog: Another Intriguing Result from Tevatron's CDF that also was analysed in Lubos blog (I don' put the link because everybody reads Lubos blog, isn't it? ;) ).
Reading the entries, and the comments one sees that there is a main natural candidate for both phenomena, a KK (kaluza-klein) partner of the gluon. For that KK gluon being in the right track one must be in a Randall-Sumdrum scenario. That means that if the LHC, that restart it's operation in fabruary, confirms the anomalies we would have a (very likely) confirmation of the existence of extra dimensions which would be possibly the most amazing all times experimental discovery in physics.
But don't shout Eureka still. Recently the LHC published an article advertising that they had not seen evidence of micro black holes, which is a bad thing for the R-S sceneries. Well, one wouldn't care too much about it. Microscopic B-h are not the former prediction of R-S scenaries and the paper had some drawbacks also.
Yesterday there was a paper about this R-S braneworlds proposal and it's measure in the LHC: LHC bounds on large extra dimensions based on the analysis of 3.1 inverse picobarns of LHC data that fixed new limits in the possible extent of the extra dimensions. AS far as I understand that bounds don't forbid the KK gluon as the author of the top quarks anomalies. Of course there are another possible answers to that anomalies. For example Marco Frasca claims (The Tevatron affair and the “fat” gluon )that his model of "fat gluon" could do the job (although he acknowledges that the KK gluon fits better).
Well, the thing is that if braneworlds are proved valid the motivation for weak scale SSB would be lacking (because R-S would solve the hierarchy problem), and with it the best candidates for dark matter. Still one could think that another KK particle are candidates for dark matter. But maybe the theories that unifies dark matter and dark energy would gain some points, or maybe be not, cosmology you know ;).
Monday, December 20, 2010
The ADSC/CFT bible
Today in arxiv has appeared something that I had never seen before, a whole collection of review articles devoted to a single topic, the ADS/CFT. There is an "overview" article that serves as reference of the others: Review of AdS/CFT Integrability: An Overview.
If I haven't counted bad there are 23 articles. And this is a review!. Clearly that is an indication of the fact that AdS/CfT is a very active line of research with many branches.
If I haven't counted bad there are 23 articles. And this is a review!. Clearly that is an indication of the fact that AdS/CfT is a very active line of research with many branches.
Thursday, December 02, 2010
Behind the super event horizont
This is a very brief note to tell that I have not forgotten about the blog.
There are a couple of combined reason for my long absence. Possible one of the most important ones is that my favourite (and expensive) wireless keyboard is out of work because it's USB connector seems to be slightly broken. Now I must return to writing with a wired keyboard, which is uncomfortable and it results in laziness for writing.
I also have had a few math exams, which take time out, I have been busy with activities out of physics (doing an small software develpment, have returned to get piano lesson because of a very good economic offer, deciding which martial art I want learn now that there is no instructors here in the one I did any more, etc).
In the physics side I have been refreshing my knowledge in some topics (for example renormalization) and studying new ones. Specially I am very involved in black hole physic. Both in classical semiclassical gravity (dynamic horizons, vadya metrics, etc) with the idea of see if it is possible to realize some idea I have about "entropic force" effects in black hole physics. Also I am haveing a close attention to a somewhat technical points of black holes in supergravity and string theory, far beyond the basic (although very important) results of the nineties that appear in most books. I hope that these two areas could result in something useful, but who know?
Anyway, I am recovering from the trauma that has supposed the dead of my favourite keyboard and hopefully I'll return to write more often here.
Tuesday, October 05, 2010
Where to hide a vacuum?
This last mounth happened many interesting things and there were a few good papers. Possibly I´l mention some of them in the future, but today just want to write a brief entry about a pre-idea.
The energy of vacuum is an ugly problem for QFT and string theory. Both in the theoretical side, the vacuum energy would be a lot greater than 0, and in the experimental side, the universe seems to be accelerating according to the famous last nineties observations. The observational side is less worrying: It is due to an imbalance among redshifth and brightness of supernovae. Well, one could try to imaginate an missing light theory (MLT) where some photons are lost in the travel from the distant supernovae to us. This would result in a lost of intensity that could explain the observations. The way to "loose photons" would be by means that some (very rare, of course) interaction with K gravitons in a warped scenario, or in F-theory like scenaries where unification of gauge bossons is in upper dimensional branes one could try to search ways to loose some photon in that branes. Ok, this an idea of myself, and I have not purchased it too much, there are good reasons to think it is not an excellent/important idea.
Or it could be that the accelerated expansios is real but not due to a cosmological constant. One way would be the entropic force scenarie of Gerge Smooth where the acceleration is due to a entropic force caused by the entropy of the cosmological horizon. Or, maybe some "dark energy" theorie.
All of those phenomemenological problems and solutions don't address the fundamental problem that there is a vacuum energy in QFT that should be great. The most extended way is a"landscape + antropic" solution based on the Weimberg ideas and developed by Polchinsky, Bousso, etc and has derived in the multiverse scenario.
Reading the articles in the CC problem (for example, this of WItten: The Cosmological Constant From The Viewpoint Of String Theory or this other of Polchinsky: The Cosmological Constant and the String Landscape ) one can learn that the main objective is to get an small vacuum energy. But I thin that there is another alternative. To put the vacuum energy out of the reach of gravity. That sound like a hard problem because gravity couples to everything, that seems to be one of the most imprtant insights of general relativity. Well, of course I have not a mechanism to hide the vacuum energy for gravity or I would be trying to publish the paper where I develop it to some important review (and it would be in the arxiv just now), butt he key point is that if there is a way to do so it would give an elegant solution to a long standing problem and it could be, possibly, consistent with all the cosmological constraints, including accelerated expansion, inflation, CMB, etc. Well, maybe one could try to relate the mechanism to the observation that some people has made among the CC (presumably) observed value and the neutrino masses. Or, better, to try to relate it to the (presumably) recent observation of different masses among a neutrino and an antineutrino.Or one could forget neutrinos at all, of course.
Well, it is a pre-idea, as I said. For the most conservative readers my recommendation is to look at the two papers I linked (if they haven't already made it) and forget my comments ;-).
Monday, August 30, 2010
Verlinde videos on emergent gravity
Reading the kea's new blog I advertised that there were two videos of Verlinde talking about emergent gravity:
1)KIPT video
2) Perimeter video
At the beginning of this summer Verlinde had announced it's presence in a string theory conference in Madrid but, unfortunately, at last he didn't assist. Because of that I was curious to see in video what I missed in direct and looked at the first of the videos. The realization is somewhat poor in various moments and you can't see Verlinde typing equations in the blackboard or you can't see complete the slides. Still you can follow the conference so it is ok.
In the conference he argues some thing that dn't appear in his paper On the Origin of Gravity and the Laws of Newton. Searching on verlinde's papers n arxiv one can find that some of the things he says on the conference about Berry phase or Born-Oppenheimer/adiabatic could be somewhat rooted on this other paper: Black Hole Berry Phase
While watching the video I have got the impression that it could be interesting to see it one could get an alternative construction of general relativity using entropy instead of geometry as the way to go from special relativity, that is, constant speed reference systems, to accelerated systems. In particular I thought about it when Verlinde does sme considerations about Rindler space.
If that would be possible one would have a different way to consider the questions of general relativity. Also if that entropic viewpoint of general relativity makes sense one could use as a framework to formulate actual theories, including string theory, and, maybe, it could seed some light on it. In that sense it would be more an entropic formulation of general relativity that anything else.
Of course he last two paragraphs are just my considerations, and wouldn't be confused with what Verlinde says.
To end this entry just to mention that a few days ago Peter G.O. Freund posted the paper Emergent Gauge Fields where he argues that the entropic force scenario for gravity could mean, because of ADS/CFT, that all other forces are emergent. The paper is discussed in Peter WOits blog Everything is Emergent. Verlinde mentions similar things at the end of the talk.
Well, as I said in my previous post about entropic gravity I agree with the common view that this idea is very vague. Still I liked the talk over the paper. Even if the idea of gravity through entropy fails the talk is entertaining and worth to watch.
1)KIPT video
2) Perimeter video
At the beginning of this summer Verlinde had announced it's presence in a string theory conference in Madrid but, unfortunately, at last he didn't assist. Because of that I was curious to see in video what I missed in direct and looked at the first of the videos. The realization is somewhat poor in various moments and you can't see Verlinde typing equations in the blackboard or you can't see complete the slides. Still you can follow the conference so it is ok.
In the conference he argues some thing that dn't appear in his paper On the Origin of Gravity and the Laws of Newton. Searching on verlinde's papers n arxiv one can find that some of the things he says on the conference about Berry phase or Born-Oppenheimer/adiabatic could be somewhat rooted on this other paper: Black Hole Berry Phase
While watching the video I have got the impression that it could be interesting to see it one could get an alternative construction of general relativity using entropy instead of geometry as the way to go from special relativity, that is, constant speed reference systems, to accelerated systems. In particular I thought about it when Verlinde does sme considerations about Rindler space.
If that would be possible one would have a different way to consider the questions of general relativity. Also if that entropic viewpoint of general relativity makes sense one could use as a framework to formulate actual theories, including string theory, and, maybe, it could seed some light on it. In that sense it would be more an entropic formulation of general relativity that anything else.
Of course he last two paragraphs are just my considerations, and wouldn't be confused with what Verlinde says.
To end this entry just to mention that a few days ago Peter G.O. Freund posted the paper Emergent Gauge Fields where he argues that the entropic force scenario for gravity could mean, because of ADS/CFT, that all other forces are emergent. The paper is discussed in Peter WOits blog Everything is Emergent. Verlinde mentions similar things at the end of the talk.
Well, as I said in my previous post about entropic gravity I agree with the common view that this idea is very vague. Still I liked the talk over the paper. Even if the idea of gravity through entropy fails the talk is entertaining and worth to watch.
Monday, July 26, 2010
Higgs search at ICHEP + four interesting articles in arxiv.
The great conference of the moment is ICHEP. It has a dedicated blog where very well known people as Tommao Dorigo (quantum diaries survivor), Jester (resonances) and many others are posting about the conferences.
Today is a great day in the conference. In one hand the French president Nicolas Sarkozy will give a talk (not sure what he will speak about, possibly about the financiation of CERN) and, just after that, the Tevatron people will expose the combined D0 and CDF results concerning the Higgs search.where it will be settled the question or wetter the gossip Tomasso spread a few days go had some foundation or he will, definitively, be charged with the nickname of "the Paris Hilton of Physics" as he was referred in a previous talk of the tevatron fellowship a few days ago. I don't really like that descalifications, but maybe it was just a joke.
Anyway, you can follow those two conferences live here. The tevatron talk begins at 4 30(spanish hour).
Out of ICHEP there are interesting things also.
These weekend at least two interesting paper appeared in arxiv. On one of them Topological Influence between Monopoles and Vortices: a Possible Resolution of the Monopole Problem the authors, Shingo Kobayashi. Michikazu Kobayashi, Yuki Kawaguchi, Muneto Nitta, Masahito Ueda propose a new way to eliminate monopoles from the spectrum of grand unification theories such as SU(5) or SU(10).
That monopoles are considered an inevitable aspect of that theories, appearing in the spontaneous symmetry breaking hat leads from the unified theories to the standard model. Like monopoles are not observed some mechanism is required to explain their absence (assuming the unification of forces is a reality). The usual mechanism is thought to be inflation that dilutes their density to one in a cosmological horizon. Mathematically the presence, of that monopoles is linked to the second homotopy group, $$ \pi_2(G/H)$$, of the quotient group G/H where G is the grand unification group and H is the resulting group after symmetry breaking, being non trivial. If the subgroup H contains an U(1) them it can be shown that $$\pi_2(G/H)\cong \pi_1(H)\cong \mathbb{Z}$$.
The author claim that using the, so called, Alice strings that can possibly also appear in the GUT. They have found a loophole in the argument that leads to the monopoles non-existence (or existence of at most one monopole) Monopoles are rotated into antimonopoles if rotated along Alice Strings. Because of that in certain cases monopoles can annihilate in pairs in the presence of that strings. To analyse the question they describe a combined monopole + Alice string by means of a different type of homotopy groups, the abe group. Remember that the usual n-homotopy groups are, loosely speaing, inequivalent ways to embed an n-sphere in the target space. Abe homotopy groups are constructed in a similar way using instead of spheres pinched torus.
I don't know too much of Alice strings,beyond what is exposed in the article so while I don't read more about them I can't take a persona opinion about how reliable that loophole is. In any case the article is very well written and very elegant mathematically so it deserves to be truth more than many others simply because of that ;).
Another very interesting article of last weekend was SU(3) × SU(2) × U(1) Vacua in F-Theory by Kang-Sin Choi. The title says what it offers. The abstract clarifies it:
The Standard Model group and matter spectrum is obtained in vacua of F-theory, without resorting to an intermediate unification group. The group SU(3) x SU(2) x U(1)_Y is the commutant to SU(5)_t \times U(1)_Y structure group of a Higgs bundle in E_8 and is geometrically realized as a deformation of I_5 singularity. Lying along the unification groups of E_n, our vacua naturally inherit their unification structure. By modding SU(5)_t out by Z_4 monodromy group, we can distinguish Higgses from lepton doublets by matter parity. Turning on universal G-flux on this part, the spectrum contains three generations of quarks and leptons, as well as vectorlike pairs of electroweak and colored Higgses. Minimal Yukawa couplings is obtained at the renormalizable level.
I will add that not depending on an unification group the monopoles existences is also ruled out. In fact in F-theory GUTs the gauge groups live in different number of dimensions that matter fermions. I never have stopped to think if that has any influence in the monopoles prediction, but I guess not so this kind of scenario, without unification, solves that problem. In fact semirealistic standard model can be obtained in string theory in heterotic or branneworld construction, so it is nt exclusive of F-theory. That spoils the former idea of the eighties of string theory as a generalization of the grand unification schemes but it doesn't mean string theory fails, of course.
Today also have appeared at least two very interesting papers. In this case both share an author, Tom Banks. One of them is TASI Lectures on Holographic Space-Time, SUSY and Gravitational Effective Field Theory and it's abstract says:
I argue that the conventional field theoretic notion of vacuum state is not valid in quantum gravity. The arguments use gravitational effective field theory, as well as results from string theory, particularly the AdS/CFT correspondence. Different solutions of the same low energy gravitational field equations correspond to different quantum systems, rather than different states in the same system. I then introduce {\it holographic space-time} a quasi-local quantum mechanical construction based on the holographic principle. I argue that models of quantum gravity in asymptotically flat space-time will be exactly super-Poincare invariant, because the natural variables of holographic space-time for such a system, are the degrees of freedom of massless superparticles. The formalism leads to a non-singular quantum Big Bang cosmology, in which the asymptotic future is required to be a de Sitter space, with cosmological constant (c.c.) determined by cosmological initial conditions. It is also approximately SUSic in the future, with the gravitino mass $K \Lambda^{1/4}
The other is Pedagogical notes on black holes, de Sitter space, and bifurcated horizons and this is its abstract:
I discuss black hole evaporation in two different coordinate systems and argue that the results of the two are compatible once one takes the holographic principle into account. de Sitter space is then discussed along similar lines. Finally I make some remarks about smooth initial conditions in GR, which evolve to space-times with bifurcate horizons, and emphasize the care one must take in identifying spaces of solutions of General Relativity which belong to the same quantum theory of gravity. No really new material is presented, but the point of view I take on all 3 subjects is not widely appreciated.
I am just reading the first, so I can't say too much about them just now. moreover, if my memory is right banks was the thesis director of Lubos Motl so one would expect that he will write about these articles if the climate wars, or maybe the Higgs search announcement of today, allow him to do so. If not maybe I will edit this entry to say something about the first of the bank's articles that looks really intriguing.
P.S. IMPORTANT NOTE: I have just realized that there seems to be a problem with the template of the blog and that latex is not working any more in these, and all the other, entries. I'll try to see if the probem can be fixed.
Today is a great day in the conference. In one hand the French president Nicolas Sarkozy will give a talk (not sure what he will speak about, possibly about the financiation of CERN) and, just after that, the Tevatron people will expose the combined D0 and CDF results concerning the Higgs search.where it will be settled the question or wetter the gossip Tomasso spread a few days go had some foundation or he will, definitively, be charged with the nickname of "the Paris Hilton of Physics" as he was referred in a previous talk of the tevatron fellowship a few days ago. I don't really like that descalifications, but maybe it was just a joke.
Anyway, you can follow those two conferences live here. The tevatron talk begins at 4 30(spanish hour).
Out of ICHEP there are interesting things also.
These weekend at least two interesting paper appeared in arxiv. On one of them Topological Influence between Monopoles and Vortices: a Possible Resolution of the Monopole Problem the authors, Shingo Kobayashi. Michikazu Kobayashi, Yuki Kawaguchi, Muneto Nitta, Masahito Ueda propose a new way to eliminate monopoles from the spectrum of grand unification theories such as SU(5) or SU(10).
That monopoles are considered an inevitable aspect of that theories, appearing in the spontaneous symmetry breaking hat leads from the unified theories to the standard model. Like monopoles are not observed some mechanism is required to explain their absence (assuming the unification of forces is a reality). The usual mechanism is thought to be inflation that dilutes their density to one in a cosmological horizon. Mathematically the presence, of that monopoles is linked to the second homotopy group, $$ \pi_2(G/H)$$, of the quotient group G/H where G is the grand unification group and H is the resulting group after symmetry breaking, being non trivial. If the subgroup H contains an U(1) them it can be shown that $$\pi_2(G/H)\cong \pi_1(H)\cong \mathbb{Z}$$.
The author claim that using the, so called, Alice strings that can possibly also appear in the GUT. They have found a loophole in the argument that leads to the monopoles non-existence (or existence of at most one monopole) Monopoles are rotated into antimonopoles if rotated along Alice Strings. Because of that in certain cases monopoles can annihilate in pairs in the presence of that strings. To analyse the question they describe a combined monopole + Alice string by means of a different type of homotopy groups, the abe group. Remember that the usual n-homotopy groups are, loosely speaing, inequivalent ways to embed an n-sphere in the target space. Abe homotopy groups are constructed in a similar way using instead of spheres pinched torus.
I don't know too much of Alice strings,beyond what is exposed in the article so while I don't read more about them I can't take a persona opinion about how reliable that loophole is. In any case the article is very well written and very elegant mathematically so it deserves to be truth more than many others simply because of that ;).
Another very interesting article of last weekend was SU(3) × SU(2) × U(1) Vacua in F-Theory by Kang-Sin Choi. The title says what it offers. The abstract clarifies it:
The Standard Model group and matter spectrum is obtained in vacua of F-theory, without resorting to an intermediate unification group. The group SU(3) x SU(2) x U(1)_Y is the commutant to SU(5)_t \times U(1)_Y structure group of a Higgs bundle in E_8 and is geometrically realized as a deformation of I_5 singularity. Lying along the unification groups of E_n, our vacua naturally inherit their unification structure. By modding SU(5)_t out by Z_4 monodromy group, we can distinguish Higgses from lepton doublets by matter parity. Turning on universal G-flux on this part, the spectrum contains three generations of quarks and leptons, as well as vectorlike pairs of electroweak and colored Higgses. Minimal Yukawa couplings is obtained at the renormalizable level.
I will add that not depending on an unification group the monopoles existences is also ruled out. In fact in F-theory GUTs the gauge groups live in different number of dimensions that matter fermions. I never have stopped to think if that has any influence in the monopoles prediction, but I guess not so this kind of scenario, without unification, solves that problem. In fact semirealistic standard model can be obtained in string theory in heterotic or branneworld construction, so it is nt exclusive of F-theory. That spoils the former idea of the eighties of string theory as a generalization of the grand unification schemes but it doesn't mean string theory fails, of course.
Today also have appeared at least two very interesting papers. In this case both share an author, Tom Banks. One of them is TASI Lectures on Holographic Space-Time, SUSY and Gravitational Effective Field Theory and it's abstract says:
I argue that the conventional field theoretic notion of vacuum state is not valid in quantum gravity. The arguments use gravitational effective field theory, as well as results from string theory, particularly the AdS/CFT correspondence. Different solutions of the same low energy gravitational field equations correspond to different quantum systems, rather than different states in the same system. I then introduce {\it holographic space-time} a quasi-local quantum mechanical construction based on the holographic principle. I argue that models of quantum gravity in asymptotically flat space-time will be exactly super-Poincare invariant, because the natural variables of holographic space-time for such a system, are the degrees of freedom of massless superparticles. The formalism leads to a non-singular quantum Big Bang cosmology, in which the asymptotic future is required to be a de Sitter space, with cosmological constant (c.c.) determined by cosmological initial conditions. It is also approximately SUSic in the future, with the gravitino mass $K \Lambda^{1/4}
The other is Pedagogical notes on black holes, de Sitter space, and bifurcated horizons and this is its abstract:
I discuss black hole evaporation in two different coordinate systems and argue that the results of the two are compatible once one takes the holographic principle into account. de Sitter space is then discussed along similar lines. Finally I make some remarks about smooth initial conditions in GR, which evolve to space-times with bifurcate horizons, and emphasize the care one must take in identifying spaces of solutions of General Relativity which belong to the same quantum theory of gravity. No really new material is presented, but the point of view I take on all 3 subjects is not widely appreciated.
I am just reading the first, so I can't say too much about them just now. moreover, if my memory is right banks was the thesis director of Lubos Motl so one would expect that he will write about these articles if the climate wars, or maybe the Higgs search announcement of today, allow him to do so. If not maybe I will edit this entry to say something about the first of the bank's articles that looks really intriguing.
P.S. IMPORTANT NOTE: I have just realized that there seems to be a problem with the template of the blog and that latex is not working any more in these, and all the other, entries. I'll try to see if the probem can be fixed.
Tuesday, July 13, 2010
Brief note: a warpdrive to vixra and some recent tantalizing experimental resuts
WARPDRIVES
Reading this post at the vixra bog I got aware of this paper:
Warp Drive Basic Science Written For ”Aficionados”.Chapter II - Jose Natario.
Warp drives are a nice idea. They are inspired by the TV and cinema serial Star Trek of which I am not a particular fan, although I have seen a few chapters and most of the movies.
The key concept is that when you want to to go from a point A to a point B you contract the space in front of you and expand the one behind you. in that way it is possible to go from A to B in an arbitrary small amount of time as far as one can contract/expand the space arbitrarily.
This wordy idea was first formalized by Alcubierre in pure GR framework. The construction of the warp-drive solution requires the use NEC (null energy condition) violating matter as much as wormholes or other exotic solution in GR require.
The last I read (sorry, I don't remember the actual link) of the alcubierre solution was that the back reaction of quantum effects ruined it (or at least it's use as a time machine).
The article I link here focuses in a different kind of warp drive, the Natario warp drive. I didn't previously know of this. I have nether read the full article. What I read looks coherent (as any article in arxiv on the same subject I mean) and I don't see any particular sign of crackpottery. But it is a vixra article, that is, ii is not intended (as far as I know) to any peer to peer review so, well, you know, read it at your own risk. B.T.W. despite the name it is not written for "aficionados": At least not for the kind of aficcionados that ignore genera relativity.
EXPERIMENTAL RESULTS
Htese recent days there were an unsuall amount of experiments with surprasing results.
On of them was a result on the possible violation of the CPT symmetry by neutrinos. This was infered by the observed fact that neutrinos and antineutrinos were found t behave differently and have different mass. You can read about in, for example: MINOS: hints of CPT-violation in the neutrino sector
Another surprising result was the observed fact that in muonic atoms the proton radio decreased, contradicting QED (quantum electro dynamics).The most recent blog entry in the subject is written by "mr TGD" (no offense intended) Matti Pitkannen: The incredibly shrinking proton
And last, but not least, the rumor of a 3 sigma detection of ligh (around 115 Gev) higgs bosson in the tevatron. The last entry on the subject is own to Lubos Motl: What a light Higgs would mean for particle physics
A lot of things, and a lot of papers in arxiv today. And I have many task to do tday so I will end the entry here.
Reading this post at the vixra bog I got aware of this paper:
Warp Drive Basic Science Written For ”Aficionados”.Chapter II - Jose Natario.
Warp drives are a nice idea. They are inspired by the TV and cinema serial Star Trek of which I am not a particular fan, although I have seen a few chapters and most of the movies.
The key concept is that when you want to to go from a point A to a point B you contract the space in front of you and expand the one behind you. in that way it is possible to go from A to B in an arbitrary small amount of time as far as one can contract/expand the space arbitrarily.
This wordy idea was first formalized by Alcubierre in pure GR framework. The construction of the warp-drive solution requires the use NEC (null energy condition) violating matter as much as wormholes or other exotic solution in GR require.
The last I read (sorry, I don't remember the actual link) of the alcubierre solution was that the back reaction of quantum effects ruined it (or at least it's use as a time machine).
The article I link here focuses in a different kind of warp drive, the Natario warp drive. I didn't previously know of this. I have nether read the full article. What I read looks coherent (as any article in arxiv on the same subject I mean) and I don't see any particular sign of crackpottery. But it is a vixra article, that is, ii is not intended (as far as I know) to any peer to peer review so, well, you know, read it at your own risk. B.T.W. despite the name it is not written for "aficionados": At least not for the kind of aficcionados that ignore genera relativity.
EXPERIMENTAL RESULTS
Htese recent days there were an unsuall amount of experiments with surprasing results.
On of them was a result on the possible violation of the CPT symmetry by neutrinos. This was infered by the observed fact that neutrinos and antineutrinos were found t behave differently and have different mass. You can read about in, for example: MINOS: hints of CPT-violation in the neutrino sector
Another surprising result was the observed fact that in muonic atoms the proton radio decreased, contradicting QED (quantum electro dynamics).The most recent blog entry in the subject is written by "mr TGD" (no offense intended) Matti Pitkannen: The incredibly shrinking proton
And last, but not least, the rumor of a 3 sigma detection of ligh (around 115 Gev) higgs bosson in the tevatron. The last entry on the subject is own to Lubos Motl: What a light Higgs would mean for particle physics
A lot of things, and a lot of papers in arxiv today. And I have many task to do tday so I will end the entry here.
Wednesday, June 16, 2010
Quick note: Two proposals in breaking of the equivalence principle
Until Friday it is very unlikely that I have time to properly read the two articles that I am going to link here. But I find that they are challenging enough to leve a note abut them.
The first article was cited yesterday in the arxiv blog: New Quantum Theory Separates Gravitational and Inertial Mass (if you are Spanish and prefer reading it in that language there is a translated version by kanijo: Nueva teoría cuántica separa las masas gravitatoria e inercial.
Those entries make reference to the following arxiv paper: Inertial And Gravitational Mass In Quantum Mechanics
I haven't read the actual paper, as I said I have not too much free time this week and to be honest reading the Tech Review entry I was not too inclined to do so. But somewhat amazingly (how many probabilities are there of having such a provocative proposal two consecutive days from independent sources) the first article in arxiv hep-th of today makes a similar claim based, this time, in string theory:The influence of D-branes' backreaction upon gravitational interactions between open strings
This is the abstract:
We argue that gravitational interactions between open strings ending on D3-branes are largely shaped by the D3-branes' backreaction. To this end we consider classical open strings coupled to general relativity in Poincare AdS5 backgrounds. We compute the linear gravitational backreaction of a static string extending up to the Poincare horizon, and deduce the potential energy between two such strings. If spacetime is non-compact, we find that the gravitational potential energy between parallel open strings is independent of the strings' inertial masses and goes like 1/r at large distance r. If the space transverse to the D3-branes is suitably compactified, a collective mode of the graviton propagates usual four-dimensional gravity. In that case the backreaction of the D3-branes induces a correction to the Newtonian potential energy that violates the equivalence principle. The observed enhancement of the gravitational attraction is specific to string theory; there is no similar effect for point-particles.
It is curious how physicist use the same majestatic plural as the pope in their papers because the "we" correspond to a single author, Raphael Benichou. He has seven published articles in arxiv -being this the first one in solitary-, in different topics of string theory.
As one can suspect the violation of the principle of equivalence (PE) is only for the string living in the brane (yes, the article treats about a braneworld scenario) and it is conserved in the bulk. Well, I must say that now -reading the discussion of the article- I have just learned that this is not the first stringy paper that raises the question of the violation of the PE. Apparently the novelty is that in the previous results the rupture was based in generic effects and it applied to point particles. The result of the article is purely stringy, it resorts in features of open strings in the brane. Well, fine, but a braneworld scenario is itself very stringy in its nature and I barely can guess a good reason to have such a world if it is not in string theory. Still this effect would be doubly stringy motivated.
The set up of the paper is a toy model using D-brane models that are far away from realistic D-brane phenomenology. I didn't read the article in detail so I don't now how much the separation of the conventional gravitational potential depends on the details. Also I must say that I haven't seen an explicit mention on how weak the effect is and if there is some possibility of seeing it in an actual experiment. The fact is that what is predicted is a slower decay of the gravitational attraction at large distances (in that respect it would be something like a MOND, modified Newtonian dynamics, of the kind used to explain rotations of galaxies without the need of dark matter. I am not sure why the author doesn't say anything about this point in the discussion *). This is different from the usual result in braneword gravitational phenomenology where one looks for an increase of gravity at very small distances due to the fact that the graviton propagates in the bulk a certain very small distance.
Well, my provisional conclusion is that the first article, discussed in arxiv blog, seems to be far from being the first proposal based on "quantum gravity" of a violation of the equivalence principle. It's distinction would be that it makes not use at al of string theory, which depending on tastes could be a pus or a minus. Obviously both approaches are totally different the one of the other. I have just made a very quick view of the non stringy article and I can't comment anything about it. Probably it is easies to read for people with few or null basic in string theory. Inparticular I guess that everyone with a solid basic in QFT and GR could read it safely and take his own conclusions.
I thin that maybe Lubos will say something more about the paper later today. But there are another interesting papers in arxiv so maybe not (I seriously doubt that Distler would say anything). It is a pity that there are not actually more very active blogs by string theorist out there. I believe hat my understanding of string theory has grown enough so that what I say could have some credibility, but still it is sure that there is a lot people out there that could make a better job than me and everyone in the field would beneficiate if some of them would blog in a regular basic.
*UPDATE: Ok, seemingly my knowledge of MONDS was very outdated. Consulting wikipedia entry on MOND I see that the modern form doesn't relay on modifications of newtonian potential. In the same page it is cited an arxiv paper by bekenstein reviewing MOND that could be an interesting reading for anyone wh is curious abut MOND theories. Advise: There are many good reasons to doubt on the validity of MONDs, of course. But at least it would be good t know with certainty what it says and so avoid trivial mistakes ;).
The first article was cited yesterday in the arxiv blog: New Quantum Theory Separates Gravitational and Inertial Mass (if you are Spanish and prefer reading it in that language there is a translated version by kanijo: Nueva teoría cuántica separa las masas gravitatoria e inercial.
Those entries make reference to the following arxiv paper: Inertial And Gravitational Mass In Quantum Mechanics
I haven't read the actual paper, as I said I have not too much free time this week and to be honest reading the Tech Review entry I was not too inclined to do so. But somewhat amazingly (how many probabilities are there of having such a provocative proposal two consecutive days from independent sources) the first article in arxiv hep-th of today makes a similar claim based, this time, in string theory:The influence of D-branes' backreaction upon gravitational interactions between open strings
This is the abstract:
We argue that gravitational interactions between open strings ending on D3-branes are largely shaped by the D3-branes' backreaction. To this end we consider classical open strings coupled to general relativity in Poincare AdS5 backgrounds. We compute the linear gravitational backreaction of a static string extending up to the Poincare horizon, and deduce the potential energy between two such strings. If spacetime is non-compact, we find that the gravitational potential energy between parallel open strings is independent of the strings' inertial masses and goes like 1/r at large distance r. If the space transverse to the D3-branes is suitably compactified, a collective mode of the graviton propagates usual four-dimensional gravity. In that case the backreaction of the D3-branes induces a correction to the Newtonian potential energy that violates the equivalence principle. The observed enhancement of the gravitational attraction is specific to string theory; there is no similar effect for point-particles.
It is curious how physicist use the same majestatic plural as the pope in their papers because the "we" correspond to a single author, Raphael Benichou. He has seven published articles in arxiv -being this the first one in solitary-, in different topics of string theory.
As one can suspect the violation of the principle of equivalence (PE) is only for the string living in the brane (yes, the article treats about a braneworld scenario) and it is conserved in the bulk. Well, I must say that now -reading the discussion of the article- I have just learned that this is not the first stringy paper that raises the question of the violation of the PE. Apparently the novelty is that in the previous results the rupture was based in generic effects and it applied to point particles. The result of the article is purely stringy, it resorts in features of open strings in the brane. Well, fine, but a braneworld scenario is itself very stringy in its nature and I barely can guess a good reason to have such a world if it is not in string theory. Still this effect would be doubly stringy motivated.
The set up of the paper is a toy model using D-brane models that are far away from realistic D-brane phenomenology. I didn't read the article in detail so I don't now how much the separation of the conventional gravitational potential depends on the details. Also I must say that I haven't seen an explicit mention on how weak the effect is and if there is some possibility of seeing it in an actual experiment. The fact is that what is predicted is a slower decay of the gravitational attraction at large distances (in that respect it would be something like a MOND, modified Newtonian dynamics, of the kind used to explain rotations of galaxies without the need of dark matter. I am not sure why the author doesn't say anything about this point in the discussion *). This is different from the usual result in braneword gravitational phenomenology where one looks for an increase of gravity at very small distances due to the fact that the graviton propagates in the bulk a certain very small distance.
Well, my provisional conclusion is that the first article, discussed in arxiv blog, seems to be far from being the first proposal based on "quantum gravity" of a violation of the equivalence principle. It's distinction would be that it makes not use at al of string theory, which depending on tastes could be a pus or a minus. Obviously both approaches are totally different the one of the other. I have just made a very quick view of the non stringy article and I can't comment anything about it. Probably it is easies to read for people with few or null basic in string theory. Inparticular I guess that everyone with a solid basic in QFT and GR could read it safely and take his own conclusions.
I thin that maybe Lubos will say something more about the paper later today. But there are another interesting papers in arxiv so maybe not (I seriously doubt that Distler would say anything). It is a pity that there are not actually more very active blogs by string theorist out there. I believe hat my understanding of string theory has grown enough so that what I say could have some credibility, but still it is sure that there is a lot people out there that could make a better job than me and everyone in the field would beneficiate if some of them would blog in a regular basic.
*UPDATE: Ok, seemingly my knowledge of MONDS was very outdated. Consulting wikipedia entry on MOND I see that the modern form doesn't relay on modifications of newtonian potential. In the same page it is cited an arxiv paper by bekenstein reviewing MOND that could be an interesting reading for anyone wh is curious abut MOND theories. Advise: There are many good reasons to doubt on the validity of MONDs, of course. But at least it would be good t know with certainty what it says and so avoid trivial mistakes ;).
Monday, June 07, 2010
In Arxiv today: Supersymmetry breaking
Today there are some interesting papers in arxiv, although not so many as the previous Monday. Some of them are purely mathematical, or concern formal aspects.
I like formal aspects, and mathematics, but because I had some leaks on recent phenomenology I am provisionally interested in more mundane topics. One key aspect in phenomenology is supersymmetry breaking. To begin with the MSSM (minimal supersymmetricla standard model) only can get supersymmetry breaking by means of soft terms which are outside the model itself. These terms must arise by some method that generates them.
The older studied method is gravity mediates supersymmetry breaking. There the breaking os supersymmetry happens at high energies,because of gravity related mechanisms and gets communicate to the MSSM by means of moduli (that is, scalar neutral fields).
Another mechanism is gauge mediate supersymmetry breaking. There supersymmetry breaking happens in a hidden sector (in heterotic E8xE8 string theory typically the "other" E8) and gets transmitted to the visible sector by some gauge field.
Still another method is AMSB (anomaly mediatesd smmetry breaking). And there are a few more. All of theme have their own advantages and problems.
Instead of trying to give details here I will refer the readers to this paper A Comparison of Supersymmetry Breaking and Mediation Mechanisms by S.P. de Alwis where a review of the topic is made. It also includes many links to the key papers in the subject so it is a perfect way to get a proper guide to the subject if because of some reason you can´t or want to read a whole book about the subject. The review also gives references of string theoretical realizations of the mechanism, which is a great plus.
I like formal aspects, and mathematics, but because I had some leaks on recent phenomenology I am provisionally interested in more mundane topics. One key aspect in phenomenology is supersymmetry breaking. To begin with the MSSM (minimal supersymmetricla standard model) only can get supersymmetry breaking by means of soft terms which are outside the model itself. These terms must arise by some method that generates them.
The older studied method is gravity mediates supersymmetry breaking. There the breaking os supersymmetry happens at high energies,because of gravity related mechanisms and gets communicate to the MSSM by means of moduli (that is, scalar neutral fields).
Another mechanism is gauge mediate supersymmetry breaking. There supersymmetry breaking happens in a hidden sector (in heterotic E8xE8 string theory typically the "other" E8) and gets transmitted to the visible sector by some gauge field.
Still another method is AMSB (anomaly mediatesd smmetry breaking). And there are a few more. All of theme have their own advantages and problems.
Instead of trying to give details here I will refer the readers to this paper A Comparison of Supersymmetry Breaking and Mediation Mechanisms by S.P. de Alwis where a review of the topic is made. It also includes many links to the key papers in the subject so it is a perfect way to get a proper guide to the subject if because of some reason you can´t or want to read a whole book about the subject. The review also gives references of string theoretical realizations of the mechanism, which is a great plus.
Tuesday, June 01, 2010
Heterotic phenomenology
I have talked quite often in this blog about F-theory. This is partially due to "historical" reasons, that is, the F-theory GUT revolution happened recently, while this blog growth. Also the influence of a friend of mine to let learn algebraic geometry was a plus because F-theory relies a lot in that area of maths.
Of course another reason is that they are very good developed framework.
But that doesn't mean that there is not development in other areas of string theory. In particular from the eighties heterotic strings where the best candidate for a phenomenological model. Even today most books in string theory (such as the Becker- Becker-Swhartz one) use the heterotic to teach the math of compactification.
Today it has appeared an interesting paper in heterotic phenomenology so I will say a few things about the subject. Heterotic string/m-Theory models are mainly build by the compactification mechanism. In that aspect they differ from many advances in string theory phenomenology. The fact that a group of parallel N D-branes automatically give an U(n) gauge theory was an star point for building local models in which gravitational degrees of freedom can be ignored for many purposes. That derived in a lot of development of D-brane models in Type II A and type II B string models, and, later, the non-perturbative counterpart of type II-B, F theory, where in addition to D-branes one has (P,q) branes. In fact something is done about non local F-Theory models and some is made for M-theory from the duality among some F-theory and M-theory set ups. But here I am going to talk about the most conventional approach, full compactifications. I am not sure about it, but I think that the reason why not too much development in local M-theory models is because not too much is known for certain (despite the Bagger-Lambert minirevolution of two years ago) about the M-theory branes, although possibly that would apply better to type II A M-theory that to heterotic M-theory.
I am going now with some references. The article of today roots in his model of the year 2006: The Exact MSSM Spectrum from String Theory. I let here the abstract of the paper:
We show the existence of realistic vacua in string theory whose observable sector has exactly the matter content of the MSSM. This is achieved by compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line. Specifically, the observable sector is N=1 supersymmetric with gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons, each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair. Importantly, there are no extra vector-like pairs and no exotic matter in the zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge instanton moduli in the observable sector. The holomorphic SU(4) vector bundle of the observable sector is slope-stable.
The observable sector of the theory has an SU(3)C × SU(2)L × U(1)Y × U(1)B−L gauge group. The B-L additional group is beyond the MSSM, but that is not as bad as it seems as they discuss in the paper of today. Additionally they have:
Matter spectrum:
– 3 families of quarks and leptons, each with a right-handed neutrino
– 1 Higgs–Higgs conjugate pair
– No exotic matter fields
– No vector-like pairs (apart from the one Higgs pair)
3 complex structure, 3 K¨ahler, and 13 vector bundle moduli
This sector is obtained by by two steps. First a Spin(10) group can arise from the
spontaneous breaking of the observable sector E8 group by an SU(4) gauge instanton
on an internal Calabi-Yau threefold. Later The Spin(10) group is then broken by discrete Wilson lines to a gauge group containing SU(3)C × SU(2)L × U(1)Y as a factor.
The structure of the hidden sector depends on the choice of a stable, holomorphic
vector bundle V ′. The topology of V ′, that is, its second Chern class, is constrained by two conditions: first, the anomaly cancellation equation:
$$ c2(V´) = c2(TX) - c2(V) - [W] $$
Here c2 means the second Chern class of the vector bundle V and [W] is a possible effective five-brane class. Ok, 'll stop writing the details that can be read in the paper. The important part is that they don't obtain in detail the aspects of the hidden sector (the sector of the other E8 group of the E8xE8 heterotic string). They simply assume it's existence.
Since 2006 that model has been further developed and has lead to this paper today: The Mass Spectra, Hierarchy and Cosmology of B-L MSSM Heterotic Compactifications
The two papers even share one co-author, Burt A. Ovrut. The abstract reads:
The matter spectrum of the MSSM, including three right-handed neutrino supermultiplets and one pair of Higgs-Higgs conjugate superfields, can be obtained by compactifying the E_{8} x E_{8} heterotic string and M-theory on Calabi-Yau manifolds with specific SU(4) vector bundles. These theories have the standard model gauge group augmented by an additional gauged U(1)_{B-L}. Their minimal content requires that the B-L gauge symmetry be spontaneously broken by a vacuum expectation value of at least one right-handed sneutrino. In previous papers, we presented the results of a quasi-analytic renormalization group analysis showing that B-L gauge symmetry is indeed radiatively broken with an appropriate B-L/electroweak hierarchy. In this paper, we extend these results by 1) enlarging the initial parameter space and 2) explicitly calculating all renormalization group equations numerically, without approximation. The regions of the initial parameter space leading to realistic vacua are presented and the B-L/electroweak hierarchy computed over these regimes. At representative points, the mass spectrum for all sparticles and Higgs fields is calculated and shown to be consistent with present experimental bounds. Some fundamental phenomenological signatures of a non-zero right-handed sneutrino expectation value are discussed, particularly the cosmology and proton lifetime arising from induced lepton and baryon number violating interactions.
Since the 2006 paper math sophistication has grown and in the way of the theory the have used things such as monads, spectral covers or cohomological methods to calculate the texture of Yukawa couplings and other parameters. The key ingredient is still a Calabi-Yau manifolds with Z3xZ3 homotopy and a vector bundle with SU(4) structure group. The observable matter spectrum is basically the same of the previous paper. As I said before they state that: The existence of the extra U(1)BL gauge factor, far from being being extraneous or problematical, is precisely what is required to make a heterotic vacuum with SU(4) structure group phenomenologically viable. The reason is the following. As is well-known, four-dimensional N = 1 supersymmetric theories generically contain two lepton number violating and one baryon number violating dimension four operators in the superpotential. The former,
if too large, can create serious cosmological di culties, such as in baryogenesis
and primordial nucleosynthesis , as well as coming into conflict with direct measurements of lepton violating decays.
Well, the details can be read in the paper. The important thing is that the model is mature enough to allow explicit and accurate renormalization group analysis of the effective field theory and do precise predictions of some aspects.
This is not the only line of investigation in heterotic string theory. As I have stated this gives mainly an MSSM but no unification group scheme is followed. But there are such kind of constructions. As early as in 2005 there is a paper doing such a thing from heterotic M-theory: An SU(5) Heterotic Standard Model-
The authors are Vincent Bouchard, Ron Donagi. and the abstract says:
We introduce a new heterotic Standard Model which has precisely the spectrum of the Minimal Supersymmetric Standard Model (MSSM), with no exotic matter. The observable sector has gauge group SU(3) x SU(2) x U(1). Our model is obtained from a compactification of heterotic strings on a Calabi-Yau threefold with Z_2 fundamental group, coupled with an invariant SU(5) bundle. Depending on the region of moduli space in which the model lies, we obtain a spectrum consisting of the three generations of the Standard Model, augmented by 0, 1 or 2 Higgs doublet conjugate pairs. In particular, we get the first compactification involving a heterotic string vacuum (i.e. a {\it stable} bundle) yielding precisely the MSSM with a single pair of Higgs.
If one reads the paper one can see that it cites the papers in heterotic string that are the basic of the other models. This can look a bit surprising since one article is about heterotic string (which has 10 dimensions)and the other about heterotic M-theory (which has 11 dimensions). Nut they actually work with compactifications in a calaby-Yau threfold. That is because the eleventh dimension of the heterotic M-theory has an special character and no compactification of is is done. On the contrary the type II A M-theory has a more conventional eleventh dimensions and it requires compactification on G2 holonomy bundles, which are harder to work. Well, I am far from being an expert in the heterotic phenomenology, but I thought that the today paper was a good occasion to say some things about it.
Besides this paper today there has been many other interesting papers. Fortunately Lubos has written an entry doing a brief comments on them and I prefer link you to that entry to get the info: A generous hep-th Tuesday
Update: In the Lubos entry (where very gently this post is linked, thanks Lubos ;)) the papers about heterotic phenomenology have been discussed and someone posted two papers about G2 heterotic compactifications, concretelly : http://arxiv.org/abs/0810.3285 and http://arxiv.org/abs/0905.1968.
It has also been discussed an issue about the prediction of the paper considered here saying that the mass of the Higgs boson was around 101 - 106 GeV. while the LEP had excluded with a 95% confidence level a Higgs mass minor than 114 GeV. Lubos argues that 95% is not enought to exclude the value f there are goo theoretical reasons to do s. I would add that Jester (resonance) wrote a post stating that the LEP exclusion ny worked for conventional Higgs. I don't remember the details so I can't say if that is relevant, but I recommend the readers of this blog to make a search in resonances.
Of course another reason is that they are very good developed framework.
But that doesn't mean that there is not development in other areas of string theory. In particular from the eighties heterotic strings where the best candidate for a phenomenological model. Even today most books in string theory (such as the Becker- Becker-Swhartz one) use the heterotic to teach the math of compactification.
Today it has appeared an interesting paper in heterotic phenomenology so I will say a few things about the subject. Heterotic string/m-Theory models are mainly build by the compactification mechanism. In that aspect they differ from many advances in string theory phenomenology. The fact that a group of parallel N D-branes automatically give an U(n) gauge theory was an star point for building local models in which gravitational degrees of freedom can be ignored for many purposes. That derived in a lot of development of D-brane models in Type II A and type II B string models, and, later, the non-perturbative counterpart of type II-B, F theory, where in addition to D-branes one has (P,q) branes. In fact something is done about non local F-Theory models and some is made for M-theory from the duality among some F-theory and M-theory set ups. But here I am going to talk about the most conventional approach, full compactifications. I am not sure about it, but I think that the reason why not too much development in local M-theory models is because not too much is known for certain (despite the Bagger-Lambert minirevolution of two years ago) about the M-theory branes, although possibly that would apply better to type II A M-theory that to heterotic M-theory.
I am going now with some references. The article of today roots in his model of the year 2006: The Exact MSSM Spectrum from String Theory. I let here the abstract of the paper:
We show the existence of realistic vacua in string theory whose observable sector has exactly the matter content of the MSSM. This is achieved by compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line. Specifically, the observable sector is N=1 supersymmetric with gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons, each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair. Importantly, there are no extra vector-like pairs and no exotic matter in the zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge instanton moduli in the observable sector. The holomorphic SU(4) vector bundle of the observable sector is slope-stable.
The observable sector of the theory has an SU(3)C × SU(2)L × U(1)Y × U(1)B−L gauge group. The B-L additional group is beyond the MSSM, but that is not as bad as it seems as they discuss in the paper of today. Additionally they have:
Matter spectrum:
– 3 families of quarks and leptons, each with a right-handed neutrino
– 1 Higgs–Higgs conjugate pair
– No exotic matter fields
– No vector-like pairs (apart from the one Higgs pair)
3 complex structure, 3 K¨ahler, and 13 vector bundle moduli
This sector is obtained by by two steps. First a Spin(10) group can arise from the
spontaneous breaking of the observable sector E8 group by an SU(4) gauge instanton
on an internal Calabi-Yau threefold. Later The Spin(10) group is then broken by discrete Wilson lines to a gauge group containing SU(3)C × SU(2)L × U(1)Y as a factor.
The structure of the hidden sector depends on the choice of a stable, holomorphic
vector bundle V ′. The topology of V ′, that is, its second Chern class, is constrained by two conditions: first, the anomaly cancellation equation:
$$ c2(V´) = c2(TX) - c2(V) - [W] $$
Here c2 means the second Chern class of the vector bundle V and [W] is a possible effective five-brane class. Ok, 'll stop writing the details that can be read in the paper. The important part is that they don't obtain in detail the aspects of the hidden sector (the sector of the other E8 group of the E8xE8 heterotic string). They simply assume it's existence.
Since 2006 that model has been further developed and has lead to this paper today: The Mass Spectra, Hierarchy and Cosmology of B-L MSSM Heterotic Compactifications
The two papers even share one co-author, Burt A. Ovrut. The abstract reads:
The matter spectrum of the MSSM, including three right-handed neutrino supermultiplets and one pair of Higgs-Higgs conjugate superfields, can be obtained by compactifying the E_{8} x E_{8} heterotic string and M-theory on Calabi-Yau manifolds with specific SU(4) vector bundles. These theories have the standard model gauge group augmented by an additional gauged U(1)_{B-L}. Their minimal content requires that the B-L gauge symmetry be spontaneously broken by a vacuum expectation value of at least one right-handed sneutrino. In previous papers, we presented the results of a quasi-analytic renormalization group analysis showing that B-L gauge symmetry is indeed radiatively broken with an appropriate B-L/electroweak hierarchy. In this paper, we extend these results by 1) enlarging the initial parameter space and 2) explicitly calculating all renormalization group equations numerically, without approximation. The regions of the initial parameter space leading to realistic vacua are presented and the B-L/electroweak hierarchy computed over these regimes. At representative points, the mass spectrum for all sparticles and Higgs fields is calculated and shown to be consistent with present experimental bounds. Some fundamental phenomenological signatures of a non-zero right-handed sneutrino expectation value are discussed, particularly the cosmology and proton lifetime arising from induced lepton and baryon number violating interactions.
Since the 2006 paper math sophistication has grown and in the way of the theory the have used things such as monads, spectral covers or cohomological methods to calculate the texture of Yukawa couplings and other parameters. The key ingredient is still a Calabi-Yau manifolds with Z3xZ3 homotopy and a vector bundle with SU(4) structure group. The observable matter spectrum is basically the same of the previous paper. As I said before they state that: The existence of the extra U(1)BL gauge factor, far from being being extraneous or problematical, is precisely what is required to make a heterotic vacuum with SU(4) structure group phenomenologically viable. The reason is the following. As is well-known, four-dimensional N = 1 supersymmetric theories generically contain two lepton number violating and one baryon number violating dimension four operators in the superpotential. The former,
if too large, can create serious cosmological di culties, such as in baryogenesis
and primordial nucleosynthesis , as well as coming into conflict with direct measurements of lepton violating decays.
Well, the details can be read in the paper. The important thing is that the model is mature enough to allow explicit and accurate renormalization group analysis of the effective field theory and do precise predictions of some aspects.
This is not the only line of investigation in heterotic string theory. As I have stated this gives mainly an MSSM but no unification group scheme is followed. But there are such kind of constructions. As early as in 2005 there is a paper doing such a thing from heterotic M-theory: An SU(5) Heterotic Standard Model-
The authors are Vincent Bouchard, Ron Donagi. and the abstract says:
We introduce a new heterotic Standard Model which has precisely the spectrum of the Minimal Supersymmetric Standard Model (MSSM), with no exotic matter. The observable sector has gauge group SU(3) x SU(2) x U(1). Our model is obtained from a compactification of heterotic strings on a Calabi-Yau threefold with Z_2 fundamental group, coupled with an invariant SU(5) bundle. Depending on the region of moduli space in which the model lies, we obtain a spectrum consisting of the three generations of the Standard Model, augmented by 0, 1 or 2 Higgs doublet conjugate pairs. In particular, we get the first compactification involving a heterotic string vacuum (i.e. a {\it stable} bundle) yielding precisely the MSSM with a single pair of Higgs.
If one reads the paper one can see that it cites the papers in heterotic string that are the basic of the other models. This can look a bit surprising since one article is about heterotic string (which has 10 dimensions)and the other about heterotic M-theory (which has 11 dimensions). Nut they actually work with compactifications in a calaby-Yau threfold. That is because the eleventh dimension of the heterotic M-theory has an special character and no compactification of is is done. On the contrary the type II A M-theory has a more conventional eleventh dimensions and it requires compactification on G2 holonomy bundles, which are harder to work. Well, I am far from being an expert in the heterotic phenomenology, but I thought that the today paper was a good occasion to say some things about it.
Besides this paper today there has been many other interesting papers. Fortunately Lubos has written an entry doing a brief comments on them and I prefer link you to that entry to get the info: A generous hep-th Tuesday
Update: In the Lubos entry (where very gently this post is linked, thanks Lubos ;)) the papers about heterotic phenomenology have been discussed and someone posted two papers about G2 heterotic compactifications, concretelly : http://arxiv.org/abs/0810.3285 and http://arxiv.org/abs/0905.1968.
It has also been discussed an issue about the prediction of the paper considered here saying that the mass of the Higgs boson was around 101 - 106 GeV. while the LEP had excluded with a 95% confidence level a Higgs mass minor than 114 GeV. Lubos argues that 95% is not enought to exclude the value f there are goo theoretical reasons to do s. I would add that Jester (resonance) wrote a post stating that the LEP exclusion ny worked for conventional Higgs. I don't remember the details so I can't say if that is relevant, but I recommend the readers of this blog to make a search in resonances.
Monday, May 10, 2010
Uber-naturalness
The most interesting paper today n arxiv hep_th is very probably this: Uber-naturalness: unexpectedly light scalars from supersymmetric extra dimensions
This is the abstract:
Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M_KK, in extra-dimensional models, or the gravitino mass, M_3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M_g, (e.g. the string scale, M_s, in string theory) is of order the Planck mass, M_p = 10^18 GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M_g and M_p is parameterized by the (large) size of the extra dimensional volume, V (in string units), according to M_p: M_g: M_KK: M_3/2 = 1: V^{-1/2}: V^{-2/3}: V^{-1}. We find that the generic size of quantum corrections to masses is of the order of M_KK M_3/2 / M_p ~ M_p / V^{5/3}. The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M_V ~ M_p/V^{3/2} << M_3/2 << M_KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation
One of the good things of this kind of theories is that a combination of supersymmetry and large extra dimensions allow that the gravitino wouldn't be the LSP in the kind of theories where it would usually be it. That is good if the controversial results claiming the existence of dark matter of 10 GeV are confirmed. As far as I know the gavitino couldn't be the particle responsible for that kind of DM. That's bad because the gravitino is the LSP in the Vafa F-theory GUTs. But if the idea of this paper can be translated to F-theory (which after all shares some of the characteristics of the LV theories disused in this paper) it could give them the flexibility to not be immediately ruled out if the DM experiments confirm the discovering.
Obviously the interest of the paper goes beyond that particular purpose of my own concern. It is a theoretic paper of wide interest and not a phenomenologistic paper devoted to a narrow particular subject. Anyway, it is clear that if someone wants to properly appreciate this paper beyond string theory he needs a good familiarity with supersymmetry, as explained in, for example, the book of the previous entry and cosmological issues of dark matter and inflation.
Update: A litle of meditation shows an obvious obstacle to use plainly this constructions inf F-theory, The idea of this paper relies in a variant of gravity mediated supersymmetry breaking. In F-theory supersymmetry is broken bye a variant of the guidice-massiero mechanism that belongs to gauge mediated supersymmetry breaking. Worse, the very idea of F-theory GUTS relies in the gravity decoupling so it seems hard to incorporate this idea in an straightforward way. Ok, I never have claimed to be at all an expert in F-theory or phenomenology. But I fell s if my understanding of this topics is growing fast, maybe in a few centuries I could publish something worthfull ;).
This is the abstract:
Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M_KK, in extra-dimensional models, or the gravitino mass, M_3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M_g, (e.g. the string scale, M_s, in string theory) is of order the Planck mass, M_p = 10^18 GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M_g and M_p is parameterized by the (large) size of the extra dimensional volume, V (in string units), according to M_p: M_g: M_KK: M_3/2 = 1: V^{-1/2}: V^{-2/3}: V^{-1}. We find that the generic size of quantum corrections to masses is of the order of M_KK M_3/2 / M_p ~ M_p / V^{5/3}. The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M_V ~ M_p/V^{3/2} << M_3/2 << M_KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation
One of the good things of this kind of theories is that a combination of supersymmetry and large extra dimensions allow that the gravitino wouldn't be the LSP in the kind of theories where it would usually be it. That is good if the controversial results claiming the existence of dark matter of 10 GeV are confirmed. As far as I know the gavitino couldn't be the particle responsible for that kind of DM. That's bad because the gravitino is the LSP in the Vafa F-theory GUTs. But if the idea of this paper can be translated to F-theory (which after all shares some of the characteristics of the LV theories disused in this paper) it could give them the flexibility to not be immediately ruled out if the DM experiments confirm the discovering.
Obviously the interest of the paper goes beyond that particular purpose of my own concern. It is a theoretic paper of wide interest and not a phenomenologistic paper devoted to a narrow particular subject. Anyway, it is clear that if someone wants to properly appreciate this paper beyond string theory he needs a good familiarity with supersymmetry, as explained in, for example, the book of the previous entry and cosmological issues of dark matter and inflation.
Update: A litle of meditation shows an obvious obstacle to use plainly this constructions inf F-theory, The idea of this paper relies in a variant of gravity mediated supersymmetry breaking. In F-theory supersymmetry is broken bye a variant of the guidice-massiero mechanism that belongs to gauge mediated supersymmetry breaking. Worse, the very idea of F-theory GUTS relies in the gravity decoupling so it seems hard to incorporate this idea in an straightforward way. Ok, I never have claimed to be at all an expert in F-theory or phenomenology. But I fell s if my understanding of this topics is growing fast, maybe in a few centuries I could publish something worthfull ;).
Friday, April 30, 2010
Sparticles
Supersymmetry is easy, isn't it?. I have posted (in spanish) a brief introduction to the subject. And I'll make more posts abut it. I am almost sure that everyone who has passed a course in QFT can understand the basics of supersymmetry.
After all, you have a superpartner for every particle, that has opposite statistic. You have funny names for the superpartnerts. The partner of the electron is the slectron, the quark has the squark, etc. And for bosonoics fields the thing is easy also. To the photon corresponds the photino, to the gluons the gluino, to the higgs the higssino, etc.
Well, them if you remember that for every broken global symmetry there is an associated particle, the goldstone boson them you know what a goldstino is. Isn't it?
Well, if you read the book that gives title to the entry(the full title is theory and phenomenology of sparticles) you will realize that maybe the goldstino could not be exactly what you think.
And, of course, you will learn a lot more about phenomenology of N=1 supersymmetry in 4 dimensiones. That includes the MSSM, cosmology of supersymmetry models, etc, etc. The books is from 2004 (reprinted in 2007) so it is, I guess, terribly outdated. I find it a lot better option that the,somewhat similar in it's purpose, book of Michel Dine (supersymmetry and superstrings). Ok, this book doesn't cover superstring, and it has many more pages. But with the actual trend of growing interest in phenomenology, motivated by the dark matter experiments, and the beginning of operation of the LHC it looks as a good reference book to get good info about the characteristics of neutralino, methods of supersymmetry breaking or whatever.
P.S. I'll try o update the previous posts, as promised, as soon as possible.
Wednesday, April 28, 2010
Enrique Álvarez on vacuum energy decay
When I studied theoretical physics in the UAM the everybody (well, at least everybody studying he specialty of theoretical physics) favorite teacher was Enrique Álvarez. Possibly, I don't know because I never coincided with him, today Ibañez could discuss the crown, but in that times Ibañez was in CERN and didn't teach.
Particularly great was his course in an asignature devoted to classical mechanics where he explained constrained lagrangian system, and the Dirac way to deal with them. That supposed that I had not any problem in the future understanding quantization of gauge theories, string theories, BRST operators and all that which is a great advantage. Also his course in general relativity was great.
Well, I am happy to see today in arxiv an article of him totally worth to post about: http://arxiv.org/abs/1004.4867
The article makes comments, and insights, on a previous work of Polchinsky the one of the Polchinsky action)in 2007: http://arxiv.org/abs/0709.2899 (I think he talked about that topic in the strings 2008 conferences celebrated in CERN)
The idea is that in de Sitter space the vacuum is not stable in the presence of interactions among particles. I am still reading both articles so I will not comment on them now, but I will edit this post (yes, I promise xD) as soon as I read them and explain what's going on.
But I am sure that some readers of this blog, who also had Álvarez as a teacher, will not wait me and read the article themselves. After all the requisites for reading are mainly some familiarity with basic QFT and quantization on curved spaces. In fact one of the points of this post is to advise them of the existence of the article and so avoid the possibility that they would miss it.
Particularly great was his course in an asignature devoted to classical mechanics where he explained constrained lagrangian system, and the Dirac way to deal with them. That supposed that I had not any problem in the future understanding quantization of gauge theories, string theories, BRST operators and all that which is a great advantage. Also his course in general relativity was great.
Well, I am happy to see today in arxiv an article of him totally worth to post about: http://arxiv.org/abs/1004.4867
The article makes comments, and insights, on a previous work of Polchinsky the one of the Polchinsky action)in 2007: http://arxiv.org/abs/0709.2899 (I think he talked about that topic in the strings 2008 conferences celebrated in CERN)
The idea is that in de Sitter space the vacuum is not stable in the presence of interactions among particles. I am still reading both articles so I will not comment on them now, but I will edit this post (yes, I promise xD) as soon as I read them and explain what's going on.
But I am sure that some readers of this blog, who also had Álvarez as a teacher, will not wait me and read the article themselves. After all the requisites for reading are mainly some familiarity with basic QFT and quantization on curved spaces. In fact one of the points of this post is to advise them of the existence of the article and so avoid the possibility that they would miss it.
Friday, April 09, 2010
Á guide for anonymous LHC backholics
A few days ago it was published on arxiv the following paper: Black hole/string ball production, possibly at LHC
I am busy reading any, many things nowadays and I couldn't read it immediately - despite of it's few number of pages - but today, at last, I read it.
The main interest of the papers is that it makes a quick review of the ideas that lead to the proposal of black hole creation on the LHC and to it's characteristics. Most interestingly still, it gives references to the relevant literature.
One of the focus +of the paper is the way on which the Hawking radiation is expected to behave. It is said that the first expectation was that most of the radiation would be send t Kaluza-Klein models of the gaviton that scape to the bulk. In particular a paper stating that was: A Model for High Energy Scattering in Quantum Gravity (note that the article treats other aspects as well).
Later it was argued that instead there would be a lot of hawking emission into brane particles: Black Holes Radiate Mainly on the Brane . In this paper, like in the others, the treatment is semiclassical. No construction of black out of D-branes is used. Neither Hawking radiation is described by string theory objects. Such descriptions exist, to a certain extent, but are not developed enough to use them in this contexts. In fat an analytic description of a black hole in braneworlds is inexistent even in classical gravity and some reasonable approximations have to be made. This approximations are valid for small black holes whose size is much smaller than the length of the extra dimension.
The amount of radiation send to the bulk or to the brane is important. If all the radiation is send to the brane no Hawking radiation would be observed in the LHC.
Well. I think that this article is citing mainly orthodox string theory friendly papers. Be aware that other people argue that a microcanonical statistical ensemble would be necessary. In that assumptions the lifetime of the back holes could be large enough to leave the detectors (but still there woulld, of course, no danger of earth swallowing black holes).
The theme of black hole emission has behind it a lot of publications and many, many, possibilities have been conjectured. One of that is the possibility of formation of a "cromosphere" or an "electrosphere". By that it is understood that the hawking radiation reorganizes into a permanent orbiting matter that obstruct the rest of the outgoing radiation to some extent. A recent paper in arxiv (sorry, I have no time to search the reference now) argues against it.
Also there have been more exotic ideas. For example Louis Crane abrogate for the possibility of creating black holes by collapsing large clouds of dust, of a few tons, by means of implosions. He argues that the resulting black hole would emit in supersymmetric modes and that the radiation could be modulated to use the black hole as a device to impulsate spaceships able to go into other solar systems. I have discussed this, and the one of microcanonical ensembles, possibility in my other blog. You can search there for them (if you speak Spanish).
As the readers could guess some of the suggestions in the literature have more wide acceptation, possible with very good reasons, that others. And, except for the Louis Crane idea, all depends on braneworld sceneries. Recently there was an article in arxiv that gives a wide sight into realizations of that models into full string theory. When I would have read it I'll try to summarize some of the proposals here.
UPDATE: Today Lubos has commented about an article treating black holes: Kerr black hole: the CFT entropy works for all M,J. Of course it is worth reading.
I am busy reading any, many things nowadays and I couldn't read it immediately - despite of it's few number of pages - but today, at last, I read it.
The main interest of the papers is that it makes a quick review of the ideas that lead to the proposal of black hole creation on the LHC and to it's characteristics. Most interestingly still, it gives references to the relevant literature.
One of the focus +of the paper is the way on which the Hawking radiation is expected to behave. It is said that the first expectation was that most of the radiation would be send t Kaluza-Klein models of the gaviton that scape to the bulk. In particular a paper stating that was: A Model for High Energy Scattering in Quantum Gravity (note that the article treats other aspects as well).
Later it was argued that instead there would be a lot of hawking emission into brane particles: Black Holes Radiate Mainly on the Brane . In this paper, like in the others, the treatment is semiclassical. No construction of black out of D-branes is used. Neither Hawking radiation is described by string theory objects. Such descriptions exist, to a certain extent, but are not developed enough to use them in this contexts. In fat an analytic description of a black hole in braneworlds is inexistent even in classical gravity and some reasonable approximations have to be made. This approximations are valid for small black holes whose size is much smaller than the length of the extra dimension.
The amount of radiation send to the bulk or to the brane is important. If all the radiation is send to the brane no Hawking radiation would be observed in the LHC.
Well. I think that this article is citing mainly orthodox string theory friendly papers. Be aware that other people argue that a microcanonical statistical ensemble would be necessary. In that assumptions the lifetime of the back holes could be large enough to leave the detectors (but still there woulld, of course, no danger of earth swallowing black holes).
The theme of black hole emission has behind it a lot of publications and many, many, possibilities have been conjectured. One of that is the possibility of formation of a "cromosphere" or an "electrosphere". By that it is understood that the hawking radiation reorganizes into a permanent orbiting matter that obstruct the rest of the outgoing radiation to some extent. A recent paper in arxiv (sorry, I have no time to search the reference now) argues against it.
Also there have been more exotic ideas. For example Louis Crane abrogate for the possibility of creating black holes by collapsing large clouds of dust, of a few tons, by means of implosions. He argues that the resulting black hole would emit in supersymmetric modes and that the radiation could be modulated to use the black hole as a device to impulsate spaceships able to go into other solar systems. I have discussed this, and the one of microcanonical ensembles, possibility in my other blog. You can search there for them (if you speak Spanish).
As the readers could guess some of the suggestions in the literature have more wide acceptation, possible with very good reasons, that others. And, except for the Louis Crane idea, all depends on braneworld sceneries. Recently there was an article in arxiv that gives a wide sight into realizations of that models into full string theory. When I would have read it I'll try to summarize some of the proposals here.
UPDATE: Today Lubos has commented about an article treating black holes: Kerr black hole: the CFT entropy works for all M,J. Of course it is worth reading.
Tuesday, March 30, 2010
LHC live webcast
Today at 8 30 it was expected that the LHC would make the first collisions at 7 TeV. There has been some problem and one of the beans has been lost. It is expected that around 11 a second try would be made.
You can follow the events in real time in the live webcast
You can follow the events in real time in the live webcast
Thursday, March 18, 2010
Strings 2010
I have been reading in the internet about the strings 2010, which this year has place in Texas, for a while. But I had not paid too much attention because I thought that, as usually, the event would be in summer.
Today I have been shocked when I saw a quick note in U duality blog saying that the conferences have been going this week.
This wee I was not particularly busy and if I just would have read carefully the dates I could have seen the livecast (available here).
Well, I still can see the slides of the talks of the past three days and the remaining ones (if the livecast works properly).
Well, at least I can see that still are very important people pending so it still there is some fun.
The most amazing of this is the total absence of mentions to the conferences in the everybody's favorite string theory superhero. Seemingly some global warming supervillian has taken him out from his usual missions ;).
Other than this in the meantime from the last post there has been an announcement about possible dark matter detection (you can read it in resonances, shores of the Dirac sea and , the older entry, in Lubos blog. I am planing to write my own entry, in Spanish, in my other blog).
Also Smoot et all published their second paper applying, as announced, their idea of an entropic force due to CEH(cosmic event horizons)to inflation. I'll post about it sometime in the near future. In particular I'll see if I can say something on how that idea could work together with dynamical horizons formalism for black holes and if it could somewhat influence the picture of black hole evaporation.
Of course there have been other interesting papers. For example a few authors took the F-theory GUT's strategy (that is, phenomenology using local models) to construct an MSSM from F-theory. Certainly it doesn't look that great compared with GUT, but if the dark matter detection is true, and the detected particle is something similar to a neutralino that MSSM F-theoretic scenery could be most easily compatible with that discovery than the GUT. As far as I have been able to think about it one possibility- taken account that in a certain sense F-theory GUTS are a universal extra dimension for the gauge bosons, that is, they live in a 7-brane- would be to seek Kaluza-Klein dark matter. The problem is that the involved gauge bosons are the unification ones and not the electroweaks,as it would be required for viable light dark matter. Well, maybe there are workarounds.
Also I wonder how the Smoot proposal, if admitted truth,could relax the conditions of the Vafa GUT (some of them are related to cosmology) to allow a better fit with a possible neutralino. In fact I would like to be able to analyze that kind of questions myself, but I still need to learn more in detail these questions.A good thing is that since I have the tablet PC I am advancing a lot faster. The point is that these, and for sure others, questions are worth of investigation (they are very close to measurable phenomena). As fr as I see they are much more realistic lines of research that the Verlinde proposal, which still has a good echo in arxiv. Possibly the ultimate reason behind it is not the quality and viability of the ideas but simple the difficulty of them. Easier research have more followers, simply because they offer more published papers, and them academic positions.
That is not exclusive of physic. A friend of me told me that the same thing happens in maths. Well, I understand that this thing happen. But maybe it would be good for science if the academy wouldn't be the only way to go. Or at least if it wouldn't be so burocrathic and there would be intermediate ways in which people could do some paid work in high end physics, at least sometimes, proved that the work is reasonably good. Well, I know it is not going to happen so it doesn't worth to loose time with the idea.
P.S. I'll edit the entry to ad the lacking links when I have a while for it.
Today I have been shocked when I saw a quick note in U duality blog saying that the conferences have been going this week.
This wee I was not particularly busy and if I just would have read carefully the dates I could have seen the livecast (available here).
Well, I still can see the slides of the talks of the past three days and the remaining ones (if the livecast works properly).
Well, at least I can see that still are very important people pending so it still there is some fun.
The most amazing of this is the total absence of mentions to the conferences in the everybody's favorite string theory superhero. Seemingly some global warming supervillian has taken him out from his usual missions ;).
Other than this in the meantime from the last post there has been an announcement about possible dark matter detection (you can read it in resonances, shores of the Dirac sea and , the older entry, in Lubos blog. I am planing to write my own entry, in Spanish, in my other blog).
Also Smoot et all published their second paper applying, as announced, their idea of an entropic force due to CEH(cosmic event horizons)to inflation. I'll post about it sometime in the near future. In particular I'll see if I can say something on how that idea could work together with dynamical horizons formalism for black holes and if it could somewhat influence the picture of black hole evaporation.
Of course there have been other interesting papers. For example a few authors took the F-theory GUT's strategy (that is, phenomenology using local models) to construct an MSSM from F-theory. Certainly it doesn't look that great compared with GUT, but if the dark matter detection is true, and the detected particle is something similar to a neutralino that MSSM F-theoretic scenery could be most easily compatible with that discovery than the GUT. As far as I have been able to think about it one possibility- taken account that in a certain sense F-theory GUTS are a universal extra dimension for the gauge bosons, that is, they live in a 7-brane- would be to seek Kaluza-Klein dark matter. The problem is that the involved gauge bosons are the unification ones and not the electroweaks,as it would be required for viable light dark matter. Well, maybe there are workarounds.
Also I wonder how the Smoot proposal, if admitted truth,could relax the conditions of the Vafa GUT (some of them are related to cosmology) to allow a better fit with a possible neutralino. In fact I would like to be able to analyze that kind of questions myself, but I still need to learn more in detail these questions.A good thing is that since I have the tablet PC I am advancing a lot faster. The point is that these, and for sure others, questions are worth of investigation (they are very close to measurable phenomena). As fr as I see they are much more realistic lines of research that the Verlinde proposal, which still has a good echo in arxiv. Possibly the ultimate reason behind it is not the quality and viability of the ideas but simple the difficulty of them. Easier research have more followers, simply because they offer more published papers, and them academic positions.
That is not exclusive of physic. A friend of me told me that the same thing happens in maths. Well, I understand that this thing happen. But maybe it would be good for science if the academy wouldn't be the only way to go. Or at least if it wouldn't be so burocrathic and there would be intermediate ways in which people could do some paid work in high end physics, at least sometimes, proved that the work is reasonably good. Well, I know it is not going to happen so it doesn't worth to loose time with the idea.
P.S. I'll edit the entry to ad the lacking links when I have a while for it.
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