Hep-th papers on Tuesday(adsbygoogle = window.adsbygoogle || []).push({});

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http://motls.blogspot.com/2006/05/hep-th-papers-on-tuesday.html

Let me summarize each of the 24 hep-th papers that appeared last night.

Freed, Moore, and Segal argue that the electric and magnetic fluxes on a

spacetime manifold can't be measured simultaneously because of a version

of the uncertainty principle. That should not be unexpected. Only the

electric potential or the magnetic potential may be chosen as a

fundamental degree of freedom which makes their fluxes well-defined for a

given configuration: the fluxes of the dual field are then undetermined.

Moreover, the authors argue that the uncertainty principle only applies to

torsion classes. One of the implications is that the K-theory class of the

Ramond-Ramond fields can't be physically measured. There also exists a

less mathematically formal version of that paper even though I am a bit

confused which of the two is addressed to the physicists. The insights

have special consequences for self-dual form fields; they're connected

with Pontrjagin classes.

Ben Craps offers the written version of his CERN lectures about

big-bang-like singularities in string theory. He reviews the role of the

winding modes, the Milne orbifold, attempts to use the AdS/CFT

correspondence, and the matrix big bang.

Dasgupta, Grisaru, Gwyn, Katz, Knauf, and Tatar re-derive the metric

describing certain wrapped fivebranes (based on functions among which

"cot" is the most complex one). Also, they write down certain new

non-Kähler geometries, and offer you a table that relates the non-Kähler

deformations of certain backgrounds to other effects related by dualities,

something that Anke Knauf has shown us some time ago.

Washington Taylor has written a mostly non-technical review of string

field theory for a book. While it does not annoy the reader with too many

formulae, it contains many references, including the references on newest

developments, and may be viewed as a state-of-the-art summary of the

subject.

Donagi, Reinbacher, and Yau take one of the simplest Calabi-Yau manifolds,

namely the quintic hypersurface, define heterotic string theory on them,

but consider very general configurations of the gauge field (the bundle).

Using similar diagrams that were important for the recent heterotic

standard model papers, they derive things as complicated as the Yukawa

couplings of these backgrounds.

Bambah, Mahajan, and Mukku propose the non-Abelian version of an unusual

kind of unification that one of the authors proposed in the Abelian case.

What unification do we mean? It is a unification of Maxwell's theory with

fluid dynamics, speculated to be relevant for the quark-gluon plasma.

Well, I personally see no unification in that paper. What I see is some

theory that contains the Yang-Mills field (previously Maxwell) together

with an additional scalar field and a vector field, and they are coupled

in some strange way. The Republican Party and the Democratic Party exist

in the same country and interact, but that still does not make them

unified. As you can see, it seems that the entertainment value of this

paper exceeds most others (but not all of them, as you will see below).

Damiano Anselmi offers a proof (?) that general relativity is a

renormalizable theory, if defined as "acausal gravity". The first

sentences of the body of the paper indicate that the acausality is far

from being the worst thing in this proposal: the first sentence argues

that "the necessity to quantize gravity is a debatable issue". Because it

seems likely that these initial sentences play an important role and

because I personally consider a non-quantized gravity within the quantum

world to be an obvious inconsistency, I can't recommend you to read the

full paper.

Svrek and Witten study the axion decay constant "F" in various scenarios

in string theory, including M-theory on G2 manifolds, intersecting

braneworlds, heterotic M-theory, and others. Recall that the axions are

useful to explain the strong CP-problem i.e. the smallness of the QCD

theta-angle that couples to the instanton number. Also, the axions could

be relevant to describe various potentially exciting recent experiments.

However, astrophysical bounds tell you that the axions that couple to

visible matter should not be too heavy. They should be lighter than the

GUT scale or so. The authors find that this is naturally achieved only if

the visible matter lives on shrunk cycles.

Buividovich and Kuvshinov investigate gauge theories - such as QCD - using

the method of the random walk. Define the open Wilson line from a given

point in spacetime to the point "(t,0,0,0)". You will get a point in the

gauge group manifold, and you may ask what is the probability distribution

to obtain a certain particular element of the group. The heat kernel

equation on the group manifold becomes relevant.

W.F. Kao starts by saying that recently there is a growing interest in the

Kantowski-Sachs (KS) universe - a term that I've never heard of - based on

some purely higher-derivative gravity (?). While the phrase "pure

higher-derivative gravity" may sound insulting, it does not seem to play

much role in the paper. On the other hand, the KS universe seems to be

nothing else than the FRW universe with an extra dependence on the

coordinate "theta", making it anisotropic. The growing interest in this

geometry is proved by three papers from 1999, 2003, 2004. This KS Universe

is supposed to be relevant for inflation. Because I don't know where to

put this paper in my understanding of the world, I can't tell you more.

Laamara, Drissi, and Saidi want to relate topological string theory on the

conifold with the fractional quantum hall effect (FQHE). Well, there are

already quite many things that are claimed to be equivalent to topological

string theory on the conifold. The links between FQHE and fluids of

D-branes (with their characteristic non-commutativity) were investigated

by Susskind, Hellerman, Polychronakos, and others years ago, but the

conifold seems to be a novelty introduced by the present authors.

Justin David and Ashoke Sen prove the formula for the generating function

for the degeneracies of dyons of the CHL string - the kind of formulae

that Davide Gaiotto knows very well. They map the system to the D1-D5

system and use, among other tools, various properties of the modular

functions.

Delduc and Ivanov explain the origin of some dualities in supersymmetric

quantum mechanics. They're dualities between theories with the same number

of fermions and different numbers of bosons. The equivalence is shown by

gauging additional superfields.

Gherghetta and Giedt realize the Randall-Sundrum models in terms of type

IIB string theory on "AdS5 times T11" where "T11" is the base of the

conifold, equipped with probe D7-branes. The tip is governed by the

Klebanov-Strassler theory; the following region by the Klebanov-Witten

regime; and the rest is connected to a compact Calabi-Yau manifold. The

additional D7-branes provide you with bulk gauge fields - something very

popular among the RS phenomenologists. They also claim to have some purely

stringy natural predictions for physics of these models but I have not

found what they are.

R.P. Malik studies QED using the BRST formalism written in terms of

superfields. Not only that I have never heard of the "horizontality

condition", but the BRST formalism itself seems like an overkill to me if

it is applied to QED, especially in this BRST superfield formalism.

Lee and Yee construct new 7-manifolds "X" that can be multiplied by "AdS4"

to give you new solutions of M-theory. These seven-dimensional manifolds -

in fact, "tri-Sasakian" manifolds - are obtained from

twelve-real-dimensional hyperKähler manifolds. Four dimensions are lost by

a method I have not understood, and the last fifth dimension disappears by

quotienting by a U(1). They also say something about the dual CFT3 theory,

for example things that follow from their calculated volume of the

seven-manifold.

Neznamov only offers a PDF file with a few pages that only seem to contain

some trivial - but not necessarily correct - manipulation with the Dirac

gamma matrices. His following PDF paper is a bit longer but even more

entertaining. He argues that the Standard Model fermions may be massive

even without Yukawa couplings by generalizing - more precisely, by

screwing - the covariant derivative. Neznamov's covariant derivative has

the standard time-component, but the spatial component has an extra term

"inverse nabla times squared mass". Lorentz invariance, unitarity, gauge

invariance, mathematics, and common sense must be sacrificed for more

noble goals.

Hortacsu and Taskin provide more than the PDF file. They argue that in

some model, a composite spin 1 particle must interact although the spin

1/2 partons don't interact. I am not sure what they exactly claim and why

but it sounds like an attempt to violate the Weinberg-Witten theorem -

although the latter is not even cited.

Janos Polonyi wants to study the emergence of the classical limit in QED.

Well, yes, I don't quite follow what is the open question that is being

answered. At any rate, to answer "this" question, the author defines some

kind of generalized density matrix, to make the quantum theory look more

classical. Because I don't believe that anything from the quantum

character of quantum field theory has to be sacrificed to understand the

classical limit properly, I doubt that one can learn something new and

true from that paper.

Edward Shuryak discusses AdS/QCD. He claims that he was the first

discoverer of the statement that confinement in the field theory should be

described as an explicitly added potential in the AdS bulk that depends on

the holographic dimension and increases as you go away from the UV. This

picture, recently promoted by Karch et al., is certainly a natural and

qualitatively correct dual parameterization of the same effect except that

I don't know how this follows from string theory, which makes it hard to

imagine that a new precise understanding of physics of confinement.

Berenstein and Cotta look at "emergent geometry" within the AdS/CFT

context. It is an orbifold of a previous paper by David Berenstein.

David's conceptually intriguing goal is to construct the bulk geometry

from certain partons - particles that live on the moduli space of

D3-branes in flat space - that can be identified within the gauge theory.

These partons effectively repel each other which makes them arrange

themselves into the right geometry, assuming that you believe the

statistical mechanical kind of reasoning. It is a sort of cute heuristic

description of the origin of the compact part of the geometry. It would be

even more interesting if one could derive something about the moduli space

of possible geometries from this starting point.

Mintz, Farina, Maia Neto, and Rodrigues look at particle production

(controlled by the Bogoliubov coefficients) of bosons in a 1+1-dimensional

theory with a boundary where the boundary conditions interpolate between

the Neumann ones and the Dirichlet ones.

______________________________________________________________________________

E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/

eFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)

Webs: http://schwinger.harvard.edu/~motl/ [Broken] http://motls.blogspot.com/

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# Hep-th papers on Tuesday

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