Thursday, August 13, 2009

Recently on arxiv

Summertime, holidays, nothing important going on, isn't it?

Maybe, but in my opinion some recent papers on arxiv are interesting.

I am going to begin by CYBERsusy. The name can suggest some SF novel cyberpunk heroine. But not. It is an acronym for 'CohomologicallY Broken Effective Retro SUperSYmmetry'. The article is titled A new mechanism for supersymmetry breaking
in the Supersymmetric Standard Model

To break supersymmetry is a good thing and a new mechanism to do so sounds important. If, moreover, the abstract ends with "The theory also leads to a zero cosmological
constant after SUSY breaking." one could begin to feel seriously interested. Being so it was a bit amazing to see how it passed unnoticed in the "big guys" blogs (you know who they are ;-) ). So I investigated a bit and I found this old entry by Lubos: Dixon law firm: CyberSUSY.

I also found that there is a blog mantained by Jon Dixon in the theme, John Dixon: Cohomology, supersymmetry and cybersusy

Well, the Lubos article refers to an older version of the theory, maybe the new one has corrected the fails, but I guess that not too much.

Another paper that I have found intriguing is related to the cosmological constant and the expanding universe. It is this, Does Unruh radiation accelerate the universe? A novel approach to the cosmic acceleration" and it's arxiv. This is the abstract:

We present a novel mechanism for the present acceleration of the universe. We find that the temperature of the Unruh radiation perceived by the brane is not equal to the inherent temperature (Hawking temperature at the apparent horizon) of the brane universe in the frame of Dvali-Gabadadze-Porrati (DGP) braneworld model. The Unruh radiation perceived by a dust dominated brane is always warmer than the brane measured by the geometric temperature, which naturally induces an energy flow between bulk and brane based on the most sound thermodynamics principles. Through a thorough investigation to the microscopic mechanism of interaction between bulk Unruh radiation and brane matter, we put forward that an energy influx from bulk Unruh radiation to the dust matter on the brane accelerates the universe

Well, the two last papers were authored by a Lubos discredited physicist in one case and by a not well known Chinese team in the other so One can find reasonable to see no resemblance of them.

More surprising are the two next papers.

The first one is by mr. Brian "elegant universe" Green and coauthores by Daniel Kabat1;2y and Stefanos Marnerides. The title sound interesting, "Dynamical decompacti cation and Three Large Dimensions". The actual paper is this and this is the abstract:

We study string gas dynamics in the early universe and seek to realize the Brandenberger-
Vafa mechanism{a goal that has eluded earlier works{that singles out three or fewer
spatial dimensions as the number which grow large cosmologically. To this end, we
consider a dilute gas of strings on a large torus, so that strings typically interact at signifi cant impact parameters. A strong exponential suppression in the interaction rates for d > 3 spatial dimensions rejects the classical argument that string worldsheets generically only intersect in four or fewer spacetime dimensions. As a consequence of this suppression, a scan over initial conditions establishes that in the dilute regime
decompacti cation of d = 3 spatial dimensions is favored over d > 3.

Nowadays the trend seems to be bottom-up approaches where one consider the standard model as an input and looks for stringy constructions to implement it in a coherent way (this goes for intersecting brane worlds and for F-theory GUT's). But I think that still is very interesting to see how "natural" is to have a world with three macroscopic dimensions and this papers seems a good approach to answer that question.

There is another paper authored by two very well known string theorists, Joseph Polchinski and Eva Silverstein. It is this: Dual Purpose Landscaping Tools: Small Extra Dimensions in AdS/CFT.

Because my knowledge of the AdS/CFT is still limited to it's basics, the chapters in the Becker-Becker-Schwartz and Clifford Johnson books plus a not too successful reading of a few reviews I can't say too much about the relevance of the paper. But still it sounds important and I am surprised not to have read about it in the you know who blogs. Maybe it is just a question of time, who knows.

The last paper I'll link is this: The Search for a Realistic String Model at LHC The title is self-explanatory. The authors are well known people, James A. Maxin, Van E. Mayes, D.V. Nanopoulos (well, actually the last one is well known for sure).

It is about the construction of a realistic intersecting D-brane model. At first sight one could think that with the rise of the F-theory GUT models the interest on this kind of phenomenological approaches would have become somewhat outdated, but seemingly it is not the case. Possibly one of the reason is that there is a lot of literature on the subject of seeking signatures of this kind of models in the LHC. You can find many of the articles doing a search for "string hunters" on arxiv hep-th. As you can see recently there was a paper on that subject, "The LHC string hunters companion II". I am actually reading the paper that correspond to the first part. It is very illustrative on how the Randall-Sundrum sceneries are actually achieved in fully string compactifications through branes wrapped in "Swiss chase" Calabi-Yau manifolds. And it contain a lot of formulae for cross sections. I think that It can be useful to me if at last my idea about a tired light mechanism to explain the observations interpreted as accelerated universe expansion make any sense after all. Independently of that they are possibly the "state of the art" in string phenomenology out of the F-Theory GUT's and (M-)heterotic models. Possibly I'll make a dedicated post to this intersecting brane models some day. But for now I think that the reader already has a lot of papers to search for.

Tuesday, August 04, 2009

TGD in vixra

At last the pdf articles of Matti pitkanen about topological geometrodynamics have been uploaded to vixra.

If someone wants to beguin he would read Topological Geometrodynamics: Overview. Advise, despite the "overview" word in the title that pdf has 1000+ pages.

There are many other papers that the reader can find by himself in vixra.

I am aware that TGD is considered crackpot. For example Lubos said in a recent post (not specifically about TGD) that TGD only existed in Matti Pitkanen's imagination. Maybe, but I think that Matti is a nice smart guy, with a correct behaviour, and he deserves the right that someone with an accredited academic position claiming that TGD is crackpot would do a proper debunking of TGD (a reasonable part of it, it is not necessary to debug the whole 1000+ paper).

But surely I am not the right person to do such a debunking. Instead I'll debug in a separate post another paper in vixra, The Graviton Background Vs. Dark Energy. The abstract says:

In the model of low-energy quantum gravity by the author, cosmological redshifts are caused by interactions of photons with gravitons. Non-forehead collisions with gravitons will lead to an additional relaxation of any photonic flux. It gives a possibility of another interpretation of supernovae 1a data. Every massive body would be decelerated due to collisions with gravitons that may be connected with the Pioneer 10 anomaly. This mechanism needs graviton pairing and "an atomic structure" of matter for working it. Also an existence of black holes contradicts to the equivalence principle: any black hole should have a gravitational mass to be much bigger - about three orders - than an inertial one.

As the readers of this blog can deduce the author of this paper is presenting a TLT (tired light theory) as a replacement of the big bang. And the will remember that I had being considering the possibility that a TLT mechanism could be used to give and explanation of the supernovae data that is being interpreted as evidence of an accelerated expansion of the universe. I have developed a little bit more my ideas and I am not sure if they work, but as far as I see what that article says makes not special sense. I'll try to explain why in the next post.