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Hep-th papers on Tuesday

  1. Oct 11, 2006 #1
    Hep-th papers on Tuesday
    ************************
    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/ http://motls.blogspot.com/
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