Friday, November 30, 2007

Hep-th papers on Friday

Below you find descriptions of the 17 today's papers on hep-th.

Bert Schroer dedicates 50+ pages to what he calls "significant conceptual differences" between quantum mechanics and quantum field theory. Needless to say, quantum field theory is a standard example of a quantum mechanical theory and the difference between quantum field theory and other quantum mechanical theories is purely dynamical, not conceptual. What defines a quantum theory are the postulates of quantum mechanics (Hilbert space, observables given by linear operators, evolution given by a unitary operator, probabilities given by expectation values of projection operators) that hold everywhere, including quantum field theory, plus a choice of dynamics on the Hilbert space (e.g. a Hamiltonian) that depends on a theory. Quantum field theory is thus just another example. Also, all the features of the uncertainty principle and localization that hold in non-relativistic quantum mechanics of particles may be derived from quantum field theory in the appropriate limit(s). The paper is a nonsensical stream of philosophical misinterpretations, misconceptions borrowed from the "real" algebraic quantum field theory, and buzzwords.

Alikram Aliev shows that the "g=2" gyromagnetic ratio for rotating charged black holes is surprisingly universal in general relativity, regardless of the asymptotic geometry, its curvature etc.: the value remarkably coincides with the value for the electron calculated from the Dirac equation. (Non-relativistic gyroscopes have "g=1".) It becomes "g=4" when two angular momenta coincide.

Arthur Sergyeyev and Pavel Krtouš study the Klein-Gordon equation on a multi-dimensional Kerr-NUT-dS or -AdS background. They find a complete set of many commuting angular-momentum-like operators and prove that they commute. This is done purely in the first-quantized setup because the second-quantized Hilbert space of course can't have a finite complete set of commuting observables. Moreover, it can't really be interpreted in the quantum fashion because the Klein-Gordon equation (or any other relativistic equation) can't really be used as a first-quantized physical Schrödinger equation. So to summarize, it is purely a work in general relativity & classical field theory, the word "operator" should be interpreted as nothing else than a mathematical (differential) operator and it is somewhat confusing why the paper is on hep-th.

Noboru Nakanishi seems to be unfamiliar with conventional renormalization and is troubled by the quadratic divergences of the Standard Model. So he rediscovers the Pauli-Villars regularization and interprets the wrong sign as a consequence of wrong statistics of these new complex fields, rather than a negative sign of the kinetic term. The author doesn't seem to be at home with quantum field theory, as highlighted e.g. by the fact that he or she doesn't use the term "Standard Model". He only cites three (not too relevant) papers besides his own and Pauli & Villars are not among them.

James Hartle, Stephen Hawking, and Thomas Hertog offer a possible solution to a problem of the Hartle-Hawking no-boundary proposal: that it predicts a very short inflation. They show a gauge-invariant, serious, "non-anthropic" calculation whose result is to add an additional factor of exp(3N) where N is the number of e-foldings to the probability of various classical solutions: similar factors may have appeared as results of anthropic hand-waving (or ingenious anthropic prophecies, if you wish). In the relevant physical context of a stringy-like landscape, a lot of inflation, starting near a de Sitter geometry at the saddle point, then follows. Surely one of the most interesting papers today.

Ee Chang-Young, Hoil Kim, and Hiroaki Nakajima construct a matrix representation of a super Heisenberg group that occurred in a stringy two-dimensional N=(2,2) deformed superspace describing D-branes on background Ramond-Ramond fields. Just like a background B-field forces bosonic coordinates to be non-commuting, a background RR-field makes the supercoordinates non-anti-commuting even though the math and limiting procedures are somewhat less clear.

Suresh Nampuri, Prasanta K.Tripathy, Sandip P. Trivedi ask, along the lines of "Dualities versus singularities", whether T-dualities - in their case those of type IIA on K3 times a two-torus - are enough to refractionalize a black hole with large D0-D4 or D0-D6 charges and bring those charges to Cardy's limit. The answer is "Yes" for non-supersymmetric black holes and "No" for generic supersymmetric black holes. The "Yes" answer might imply that the entropy of all extremal but non-supersymmetric black holes may be calculated.

Arzumanyan and 4 more Armenian authors compute the radiation from a charge that moves along a helix. Given the fact that the typical energy they consider is 10 MeV and the topic is more relevant for condensed matter physics (dielectric materials are needed) or something else, I don't think that the otherwise interesting paper should have appeared in a high-energy archive.

Cristina Zambon attempts to incorporate the so-called jump-defect, known from the sine-Gordon model, to the affine Toda field theories which are a complementary integrable description of similar physical systems.

B.M. Zupnik studies harmonic superspaces for three-dimensional theories. Harmonic superspace is a superspace that, in addition to anticommuting coordinates, contains additional bosonic coordinates spanning quotients of groups. His particular interest is in a non-Abelian Chern-Simons theory whose manifest supersymmetry from the superspace is N=5 but is extended to N=6.

Juraj Boháčik and Peter Prešnajder study the zero-spatial-dimensional anharmonic oscillator with a quartic interaction term using non-perturbative methods due to Gelfand and Yaglom. They offer a comprehensible proof of an equation that specifies corrections for such an oscillator. Again, it is interesting but not directly relevant for high-energy physicists.

A.T. Avelar et al. study topologically unusual soliton solutions to models with a single real scalar field. Their potential is a combination of (mostly fractional) powers of the field and the topologies include lumps with flat plateux at the top and lumps on top of another lump. The fact that they mention that the results may have applications to non-linear science highlights that this should probably not be a hep-th paper.

Kwan Sik Jeong studies supersymmetry breaking in KKLT-like models. It is being assumed that the source of the breaking is in a hidden, sequestered sector. The author argues that the impact of this breaking on the visible sector can be summarized in an F-term expectation value that is universal. Ratios of vevs and logarithms of ratios of various mass scales are the only thing that appear in the ultimate key formula.

Albion Lawrence, Tobias Sander, Michael B. Schulz, Brian Wecht look at type IIB string theory on a Calabi-Yau three-fold. Their aim is to find the spectrum of auxiliary fields which is not exactly a physically unique, objective, physical question but a particular natural answer may be useful. Indeed, it is useful and they argue that the expectation values of these auxiliary fields lead to deformed CFTs that add either the H-field (a field strength for the NS-NS B-field) or an SU(3) x SU(3) structure (different tangent bundles for left-movers and right-movers). Once these things are nonzero, generic vacua are non-geometric globally (although probably geometric locally, because of their starting point), a worldsheet argument suggests. Mirror symmetry is argued to hold beyond the (2,2) worldsheet supersymmetry and worldsheet instantons are presented as more important animals when their fluxes are turned on. One of the most interesting papers.

Niklas Beisert, Denis Erkal present the spin chains arising in the AdS/CFT correspondence as very special spin chains with non-nearest-neighbor interactions that nevertheless preserve the integrability of a simpler spin chain with nearest-neighbor interactions only. They can't prove the full integrability for the interesting cases that occur in string theory but they can do so for a seemingly similar gl(n) spin chain model with longer-range interactions. The proof is technically based on checking the Serre relations for a Yangian generator. A very interesting paper.

Borun D. Chowdhury and Samir D. Mathur study the fuzzball model of black holes. Now they look at radiation by these monsters. They derive the classical radiation emitted by these classical solutions (not suppressed by hbar) by combining the Hawking radiation into (very many) unstable modes of their individual geometries. I kind of feel that this was guaranteed to work because of the standard limiting relationships between classical and quantum systems but don't worry. They argue that this means that the information is manifestly preserved in the supergravity degrees of freedom. Well, I don't have any problem with the statement that these fuzzball geometries preserve the information or may behave as ordinary horizon-free solutions. They are ordinary, after all. What is missing for me is a proof that these fuzzball geometries conspire to behave like ordinary black holes in contexts where I want to believe that the black hole description is correct, e.g. after a collapse of a star. Also, I don't see any proof that all the relevant degrees of freedom that store the information about a black hole are geometric in character.

Chris Hull and R.A. Reid-Edwards discuss similar structures as Albion Lawrence et al. above, namely non-geometric compactifications. If the monodromy in such a background is taken from the T-duality group, such a background may be made similar to a geometric one by adding the T-dual coordinates besides the normal coordinates at each point. This has been discussed many times, even on this blog, and Hitchin was the most well-known guy who has advocated this viewpoint. Hull and Reid-Edwards think that one can also construct backgrounds that are non-geometric even locally, by thinking about the double as a Drinfeld double. I don't see this statement justified in the paper.

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