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.

## Monday, July 26, 2010

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## 3 comments:

Dear Javier, I actually mostly agree with your selection of the interesting preprints.

The non-GUT Standard Model F-theory vacua are surely fun, much like my ex-advisor's musings (although I am not sure that there's something new in the new paper)...

And of course, lectures about general aspects of black hole physics may always deserve reading and comments.

Hi lubos, nice to see you here again.

I am still reading the paper about the vacuum states. Maybe here is nothing new for you, but for people whose knowledge of string theory is worst than your it can be very helpfull ;).

Concerning black holes, yes, they are surely interesting. And there are many aspects of them that can be considered.

If it is not too much to ask I would like to know your opinion about the mathematical concepts of isolated and, specially, dynamical horizons. I know that it is mostly used by the relativity and LQG people, but as far as I see, they are pure classical relativity tools that could be safely used. Despite that "neutrality" I don't see string theory people using them, is there something wrong with them? Or, simple, the string community doesn't see any use of them?

Por que no:)

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