50 years after the duality of large N gauge theories to string theories was suggested, we still do not have a constructive method to find the string dual of a given gauge theory. I will review work in progress (in collaboration with S. Kundu, T. Sheaffer and L. Yung) on two approaches to understanding this, in what should perhaps be the simplest case, namely two dimensional gauge theories. The first approach uses perturbation theory to obtain an effective stringy description of 2d QCD with very massive adjoint fermions. The second approach starts from finding a good worldsheet description for the string dual to the two dimensional pure Yang-Mills theory.

Abstract: We canonically quantise Jackiw-Teitleboim  gravity in de Sitter space, with particular attention to the problem of time.  Our results suggest an holographic interpretation  for global deSitter space, in this two dimensional setting.

Abstract: The thermodynamic interpretation of Schwarzschild black holes has a rich history spanning five decades. In 1973 Bardeen et al. derived the laws of black hole mechanics which suggested a correspondence between (i) temperature and black hole’s mass, specifically T=(8πM)^-1 and (ii) entropy and black hole area: S=A/4. In 1975 Hawking found that a Schwarzschild black hole radiates as if it were a blackbody with temperature T=(8πM)^-1. This meant that the temperature-mass relationship discovered earlier was more than a correspondence. In 1977 Gibbons and Hawking proposed the action of Euclidean Schwarzschild (which also has T=(8πM)^-1) as a means to understand black hole thermodynamics. They recovered S=A/4.  

In this talk we will test if Euclidean Schwarzschild behaves like a heat bath for quantum matter that propagates on it. For simplicity we will use matter with restricted excitations – Ising spins. We will discover that increasing M causes the spins to undergo a second order phase transition from disorder to order and that the phase transition occurs at sub-Planckian M. 

Abstract: In constructing lattice versions of physical theories, usually the spacetime symmetries are given up. This is because of the use of difference approximation of the derivative operator which does not satisfy Leibniz rule. The same is responsible for the fermion doubling problem and the associated loss of chirality. We introduce a non-local lattice derivative, hereafter to be called logarithmic discrete derivative (LDD), as it admits a logarithmic expansion in powers of the difference operator and a formal lattice integral (LI) which is inverse of LDD. The pair (LDD, LI) can be shown to satisfy the same differential and integral calculi of the continuum. We demonstrate how the pair can be used to construct lattice theories with Poincaré invariance. A striking property of the resulting model is a local correspondence which says that local equations of the continuum theory still hold true on the lattice, site-wise. Although such a construction looks very formal in position space, in momentum space the action takes a simple form which may allow for numerical simulations. We show that the same momentum space results can also be obtained by using summation, instead of LI, by using a technique involving finer lattices. Similar concept was earlier arrived at by G. Bergner while studying SLAC-type non-local derivatives. We explain how LDD is related to SLAC derivative and indicate how the new understanding of locality in position space could potentially allow for more effective use of non-local derivatives in lattice studies. Time permitting, we shall also discus a generalisation of the construction to a class of curved backgrounds and another form of the lattice derivative that achieves the same thing but takes the form of an inverse sine hyperbolic function. 

Zoom: https://uky.zoom.us/my/shapere

The finiteness of entanglement entropy in string theory has crucial implications for the information paradox, quantum gravity, and holography. In my talk, I will describe the recent progress made on establishing this finiteness. I will describe the orbifold construction appropriate for analyzing entanglement in string theory, the tachyonic divergences that one encounters and how we get a finite and calculable answer for the entanglement entropy, including ten-dimensional string theory and compactification to lower dimensions. (Based on work in collaboration with Atish Dabholkar.)

I will introduce a critical string theory in two dimensions and demonstrate that this theory, viewed as two-dimensional quantum gravity on the worldsheet, is equivalent to a double-scaled matrix integral, which provides the holographic description. The worldsheet theory consists of Liouville CFT with central charge c >= 25 coupled to timelike Liouville CFT with central charge 26-c. The double-scaled matrix integral has as its leading density of states the universal Cardy density of primaries in a two-dimensional CFT, which gives the theory its name. The talk is based on joint work with Scott Collier, Beatrix Mühlmann and Victor Rodriguez.

This is a Zoom seminar:  https://uky.zoom.us/my/shapere

We will meet in CP 303 to watch it. 

Abstract: We will discuss some known subtleties of emergent geometries from large N theories (why they are different from our normal expectation for a continuum spacetime) and discuss a way to address them. We will use matrix models as our main example. The primary tool will be an exact bosonization of nonrelativistic fermions that was discovered some time ago. 

Abstract:  I will describe extremal surfaces in de Sitter space anchored at the future boundary I+. Since such surfaces do not return, they require extra data or boundary conditions in the past (interior). In entirely Lorentzian de Sitter spacetime, this leads to future-past timelike surfaces stretching between I±. Apart from an overall −i factor (relative to spacelike surfaces in AdS) their areas are real and positive. With a no-boundary type boundary condition, the top half of these timelike surfaces joins with a spacelike part on the hemisphere giving a complex-valued area. Motivated by these, we describe two aspects of “time-entanglement” in simple toy models in quantum mechanics. One is based on a future-past thermofield double type state entangling timelike separated states, which leads to entirely positive structures. Another is based on the time evolution operator and reduced transition amplitudes, which leads to complex-valued entropy. There are close parallels with pseudo-entropy which we will clarify.