Search Talks

I begin with a brief description of the black strings in backgrounds with compact circle, the Gregory-Laflamme instability and the resulting phase transition, and the critical dimensions.Then I describe a Landau-Ginzburg thermodynamic perspective on the instability and on the order of the phase transition. Next, the approach is generalized from a circle compactification to an arbitrary torus compactification. It is shown that the transition order depends only on the number of extended dimensions. I end up with outlining several open questions and puzzles related to the outcome of the Gregory-Laflamme instability.

We discuss the properties of matter in the low temperature regime at density that may exist in the core of compact stars. Assuming that in these conditions quarks are deconfined the attractive color interaction determines the formation of Cooper pairs of quarks and the resulting quark matter has properties analogous to standard superconductors. We show that under reasonable conditions a state were Cooper pairs have non-zero total momentum is energetically favored and the resulting non-homogeneous condensate is characterized by a crystal symmetry. Studying the elastic properties of such a state we find that it behaves like a solid crystal with a very large shear modulus. Our results raise the possibility that (some) pulsar glitches may originate within the Crystalline Color Superconductor core of Neutron stars.

It has been conjectured that maximally supersymmetric SU(N) Yang-Mills theory is dual to a String Theory on asymptotically AdS_5 times S^5 backgrounds. This is known as the AdS/CFT correspondence. In this talk I will show how using one-loop calculations in the gauge theory, one can study the emergence of the dual String Theory. We will see, quite explicitly, the emergence of closed strings, D-branes, open strings and space-time itself. This is done in a reduced sector (SU(2) sector), where the gauge theory can be written as Matrix Quantum Mechanics. This simple sector provides a toy model of a non-perturbative quantum theory of gravity.

In the context of AdS/CFT, it has been recently proposed that Wilson loops in higher representation of the gauge group have a dual description in terms of D-branes in AdS_5xS^5. After reviewing this new dictionary, I will present a computation of correlators between chiral primaries of N=4 SYM and Wilson loops in large symmetric and antisymmetric representations. These correlators can be computed both in supergravity using D-branes and in gauge theory from a matrix model, with precise agreement between the two sides

Due to recent, as well as less recent, work on perturbative N=8 supergravity and N=4 super Yang-Mills in 4d, the two theories are appearing more and more closely related. These relations include similar \"MHV-rule\" constructions, one-loop structure and, perhaps, the same UV behavior, namely UV finiteness. This talk introduces some of the methods to study the relations.

Quantum gravity in an AdS space-time is described by an SU(N) Yang-Mills theory on a sphere, a bounded many-body system. We argue that in the high temperature phase the theory is intrinsically non-perturbative in the large N limit. At any nonzero value of the \\\'t Hooft coupling $lambda$, an exponentially large (in N^2) number of free theory states of wide energy range (of order N) mix under the interaction. As a result the planar perturbation theory breaks down. We argue that an arrow of time emerges and the dual string configuration should be interpreted as a stringy black hole

We will discuss applications of the recently developed twistor-space methods in perturbative quantum field-theory. The two central topics will be 1) the unitarity bootstrap approach to hard scattering amplitudes in QCD and 2) the analysis of the UV structure of N=8 supergravity.

The exact boundary states for the rolling D-brane solution in two-dimensional black hole systems will be presented.I will study the physical significance of the solution in relation to the ``tachyon-radion correspondence\" and the ``black hole - string transition\". When the alpha\' corrections become larger, when at the same time the Hawking temperature coincide with the Hagedorn temperature, the phase transition occurs and the physics changes drastically. It also suggests the universal feature of the decaying D-brane and its failure in the strong quantum regime. The talk is based on my series of works hep-th/0605013, hep-th/0507040 in collaboration with Soo-jong Rey (SNU) and Yuji Sugawara (Tokyo).