String Seminars

This series consists of talks in the area of Superstring Theory.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

 

Tuesday Mar 24, 2009
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Holographic superconductors provide tractable models for the onset of superconductivity in strongly coupled theories. They have some features in common with experimentally studied nonconventional superconductors. I will review the physics of holographic superconductors and go on to show that many such models are to be found in the string landscape of AdS_4 vacua.

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Tuesday Mar 17, 2009
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A simple model for chaotic inflation in supergravity is proposed. The model is N = 1 supersymmetric massive U(1)gauge theory via the Stuckelberg superfield and gives rise to D-term inflation with a quadratic term of inflaton in the potential. The Fayet-Iliopoulos field plays a role of the inflaton. It is also discussed to give rise to successful reheating and leptogenesis through the inflaton decay.

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Thursday Mar 05, 2009
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The Rozansky-Witten model is a topological sigma-model in three dimensions whose target is a hyper-Kahler manifold. Upon compactification to 2d it reduces to the B-model with the same target. Boundary conditions for the Rozansky-Witten model can be regarded as a 3d generalization of B-branes. While branes form a category, boundary conditions in a 3d TFT form a 2-category. I will describe the structure of this 2-category for the Rozansky-Witten model and its connection with a categorification of deformation quantization.

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Tuesday Feb 24, 2009
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Brane Tilings are known to describe the largest known class of SCFT's in 3+1 dimensions. There is a well established formalism to find AdS_5 x SE_5 duals to these SCFT's and to compare results on both sides. This talk extends this formalism to 2+1 dimensional SCFT's, living on the world volume of M2 branes, which are dual to AdS_4 x SE_7 backgrounds of M theory. The SCFT's are quiver gauge theories with 4 supercharges (N=2 in 2+1 dimensions) and Chern Simons (CS) couplings. They admit a moduli space of vacuum configurations which is a CY4 cone over SE_7.

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Tuesday Feb 10, 2009
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Motivated by recent mathematical developements in non-commutative Donaldson-Thomas theory, we construct a new statistical mechanicalmodel of crystal melting to count BPS bound states of D0 and D2 branes on a single D6 brane wrapping an arbitrary toric Calabi-Yau threefold. We also discuss the wall crossing phenomena, which are crucial for the proper understanding of the relation between the crystal melting and the topological string theory.

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Tuesday Jan 27, 2009
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We derive a universal upper bound on the weight of the lowest primary operator in any two-dimensional conformal field theory with a given central charge. Translated into gravitational language using the AdS/CFT dictionary, our result proves rigorously that the lightest massive state in any theory of 3D gravity and matter with negative cosmological constant can be no heavier than a particular function the cosmological constant and the Planck scale. For a large AdS space, the lower bound approaches the mass of the lightest BTZ black hole.

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Tuesday Jan 20, 2009
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In the past couple of years many new developments have been made in the techniques used for computing one-loop gauge theory amplitudes. These developments have mainly involved exploiting generalized unitarity techniques to construct the coefficients of the basis integral functions which make up a one-loop amplitude. I will outline these new developments along with their application to both QCD and N=8 supergravity amplitudes.

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Thursday Dec 04, 2008

In this talk I discuss methods to determine hydrodynamical dispersion relations from an extra-dimensional gravity dual wherein the metric is supported by scalar fields. Such a setup may eventually be used as a model of the strongly coupled plasma created in heavy ion collisions. I examine examples of both the shear and sound modes. The shear mode is analyzed using the black hole membrane paradigm; a calculation of the shear viscosity is reviewed, and then the calculation is extended to the next hydrodynamical order. All results agree with those found using the AdS/CFT prescription.

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Wednesday Dec 03, 2008
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Understanding dynamics of strongly coupled quantum field theories is an important problem in both condensed matter physics and high energy physics. In condensed matter systems, interacting quantum field theories can arise either at a critical point, or in a finite region of a parameter space. In the former case, massless modes arise as a result of fine tuning of external parameters, while, in the latter case, massless modes are protected by topology and/or symmetry.

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Tuesday Nov 25, 2008
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We discuss various properties of holographic mesons in a deconfined strongly coupled plasma. We show that such mesons obtain a width from a non-perturbative effect. On the string theory side this is due to open string modes on a D-brane tunneling into a black hole through worldsheet instantons. On the field theory side these instantons have the simple interpretation as heavy thermal quarks. We also comment on how this non-perturbative effect has important consequences for the phase structure of the Yang-Mills theory obtained in the classical gravity limit.

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