Today, there are twelve new papers primarily labeled as hepth papers. The first one, and one that may attract the highest number of readers, is a review of the membrane minirevolution by Klebanov and Torri. However, I will mention the remaining eleven preprints, too.
Membrane uprising: a review
The membrane minirevolution was discussed on this blog as a minirevolution long before most people noticed that there was a minirevolution going on.
Important papers by Bagger + Lambert and by Gustavsson (BLG) introduced a new, unusual ChernSimonslike theory with 16 supercharges in 2+1 dimensions. It was argued that it had to describe two coincident M2branes. It used to be thought that the CFT theories dual to Mtheory on "AdS4 x S7/G" had no Lagrangian description except that BLG found one.
Their theory  originally described in terms of 3algebras and other unnecessarily novel concepts  was really nice, nontrivial and symmetric only in the case of two coincident M2branes. Many people tried to generalize it. They eventually realized that the obvious generalizations for many M2branes either predicted ghosts or they were equivalent to Super YangMills theories or otherwise uninteresting.
The right generalization was eventually found by Aharony, Bergman, Jafferis, and Maldacena (ABJM). Unlike the BLG theory, it only had 12 supercharges. Their theory is an "U(N) x U(N)" ChernSimons theory at level "k". It describes M2branes stuck on "M^3 x R^8 / Z_k" whose nearhorizon geometry is clearly "AdS_4 x S^7 / Z_k": the "Z_k" group diagonally rotates all four complex coordinates in the transverse "R^8".
The supersymmetry is enhanced from the manifest 12 supercharges to 16 supercharges for the "k=1" or "k=2" cases. Klebanov and Torri show that new monopole operators  impurities or defects  produce the additional 12 currents that combine with the 16 currents of "U(1) x SU(4)" into 28 currents of "SO(8)", a group needed to show the presence of those 4 additional, a priori nonmanifest supercharges.
By the way, it's time for an M5brane minirevolution, too. ;)
Multicalorons
Instantons are topologically nontrivial solution in Euclidean spacetime that are localized both in space and (especially) time: they appear at one instant of time which gives them the name.
What are the calorons? Well, they must have something to do with heat. Indeed, one has a periodic Euclidean "thermal" time here. So they're instanton with a periodic time. It is also easy to see that multicalorons are calorons whose instanton charge exceeds one; it is equal to two in their case.
Nakamula and Sakaguchi discuss the Nahm equations (ADHM construction of the monopoles) in this context. If you don't know, the Nahm equations are "dM1/dt = [M2,M3]" and its cyclic permutations. The Jacobi elliptic functions appear in their exact solution. Some interesting insights are found but it's too special and mysterious a subject for me to pretend that I have been waiting for these results. ;)
Glowing rotating string
Matsuo considers bosonic string theory. He takes a highly exciting, rotating fundamental string and calculates its thermal emission. There's some similarity with the Kerr black holes' thermal behavior but if the author conjectures a full duality rather than an orderofmagnitude similarity (like in HorowitzPolchinski), then I must say that I would be skeptical about such a duality.
Noncommutative theories averaged over theta
Sami Saxell published his or her thesis. It reviews some basic facts about noncommutative field theories, SeibergWitten insights about them, and other wellknown things. When it comes to new ideas, the thesis focuses on the averaging over many values of the noncommutative parameters, meant to obtain a Lorentzinvariant theory.
Such an averaging creates problems for unitarity (it's like Coleman's calculations of the baby universes) and it seems that the author is well aware of these and similar lethal problems of theories constructed in this way but he or she still needed to write a fine enough thesis about something. ;)
Black hole instabilities in KlebanovStrassler
Butcher and Saffin discuss the bulk side of the KlebanovStrassler theory. They add a perturbation with some momentum and look what's going on. The size of the solution is stable but some perturbations are claimed to create black holes that affect the throat's tip. The authors think that some applications of the KlebanovStrassler geometry have therefore been physically unacceptable.
Nonrelativistic cold atoms from massive type IIA
Singh takes the Romans theory, i.e. a massive version of type IIA string theory in 10 dimensions, and constructs some "AdS4 x S6" solutions where the "AdS4" is Galilean, however. It is claimed that such an ugly AdSlike background is directly relevant for the AdS/AtomicPhysics duality. The other side, with cold atoms, is also ugly which is why the proposed duality has just passed one consistency check. ;)
AdS/AtomicPhysics on domain walls
Wapler studies 2+1D domain walls  coming from a kind of D5brane in this case  in a 3+1D spacetime occupied by the N=4 gauge theory via AdS/CFT. The domain wall is given a finite magnetic field, mass, and charge density. Various cyclotron, plasmon, and hydrodynamic phenomena are being calculated in this setup. That's surely a lot of fun for condensedmatter and atomic physical minds.
A bizarre "renormalization scheme"
Grange, Mathiot, Mutet, and Werner argue that a particular unusual approach to "renormalization" is very efficient for dynamics in the lightcone gauge. The "TaylorLagrange renormalization scheme" is based on some ad hoc looking restriction of the allowed test functions and they claim to eliminate the need for the "cancellation of infinities".
Although they promote the method as being very efficient at very high orders, they only truncate their reasoning to an approximation with at most two particles. At any rate, I think that this whole way of thinking is misguided. The choices made to restrict the allowed test functions are effectively equivalent to the introduction of the same uncertainties one gets in ordinary "renormalization schemes".
Moreover, I don't think that they use the term "renormalization scheme" in the standard way. Historically, the dominance of obscure papers from the 1960s and 1970s among their references doesn't look too promising.
Differential equations for CalabiYau threefolds
Santillan works on some equations written down by Fayyazuddin.
The differential equations relevant for CalabiYau threefold metrics are reduced to a mathematical problem where objects only depend on two real variables. Some equations are even claimed to become linear and the author concludes that they may even be solved in terms of elliptic functions or something like that.
Of course, such analytically solvable metrics have to be noncompact but their subclasses are nicely nonsingular and geodesically complete.
Fully SUSic solutions in N=2 SUGRA
Hristov, Looyestijn, and Vandoren look for configurations that preserve all eight supercharges in N=2, d=4 supergravity. Their diversity is obtained by different "electric gaugings" in the hypermultiplet and vector multiplet sectors. They link these SUGRA solutions to type IIB flux compactifications studied by Jeremy Michelson in 1996 and his followers.
AdS/QCD: scalar glueballs from QN modest
Miranda et al. use AdS/QCD to say something about the scalar glueballs. The answers are obtained from Green's functions of an AdS5 black hole with a dilaton softwall background. Quasiparticle peaks at low temperatures are important features; their data are equivalent to the data about the black hole quasinormal modes.
An updated review of superstring phenomenology
Massimo Bianchi wrote a somewhat sketchy introductory review of flux compactifications and various stringy braneworlds, as a celebration of the 25th anniversary of the GreenSchwarz mechanism. It is a useful review for those who want to be reminded about the basic classes of the conceivable phenomenological scenarios  qualitatively different types of compactifications  in string theory. When it comes to the experiments, Bianchi seems to be intrigued by signatures of anomalous U(1) groups.
Thursday, September 10, 2009 ... //
Review of the membrane minirevolution and other hepth papers
Vystavil
Luboš Motl
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9:50 AM



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