String Seminar

Physics & Astronomy String Seminar

Title: Hamiltonian approach to near extremal black hole physics

Abstract: Much progress has been made in recent years on understanding near-extremal black holes, primarily through the Euclidean path integral. These findings include large backreaction effects at both classical and quantum levels.  However, a Lorentzian formulation of these effects, as needed to describe black holes formed from collapse along with other dynamical processes, is not well understood. I will describe an approach to this problem based on the Hamiltonian formulation of gravity. In this formulation we can make contact with earlier Euclidean results while also generalizing to inherently Lorentzian processes like black hole formation. 

Date:
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Location:
CP 303
Event Series:

Special string seminar

NB: non-standard day and time.
 
Title: Generalized Replica Manifolds: The Tailor's Guide to Entanglement  
 
Abstract: We develop a simple framework for implementing a type of path integral "surgery" through a correlated averaging over codimension-one defects/extended operators. This technique is then used to construct replica manifolds by effectively cutting and gluing the path integral without explicitly modifying the underlying manifold. We argue that restricted forms of this averaging may be used to calculate Rényi entanglement entropy corresponding to a wide range of choices of subsystem partitioning. When the entanglement entropy being calculated in this way does not simply correspond to entanglement between sub-regions, we call the resulting objects from this surgery ``generalized replica manifolds.'' We show how this framework extends to gauge theories and, in particular, how in non‑Abelian gauge theories it establishes a connection between replica calculations of a gauge invariant notion of entanglement between color degrees of freedom and a quiver gauge theory structure. We also discuss further extensions of this framework as well as potential application to large N models and holography.
Date:
Location:
Zoom
Event Series:

String Seminar

Title: Physical instabilities and the phase of Euclidean path integrals.
Abstract: In this talk, I will discuss the phase of the Euclidean gravity path integral in the presence of a positive cosmological constant. I will begin by reviewing the gravitational partition function on the sphere and clarifying the procedure for determining its precise phase factor. Next, I will discuss how to compute the phase on product manifolds of the form $S^p\times M$, and explain how it connects to physical instabilities in the static patch of $dS_p$. For the special case $p=2$, I will comment on the relation to Jackiw-Teitelboim gravity. Time permitting, I will also mention the phase associated with Nariai solutions.
Date:
Location:
Zoom
Event Series:

String seminar: Large N Master Field Optimization for Multi-Matrix Systems

Abstract: It is shown how large N properties of multi-matrix systems can be obtained by minimization of a loop truncated effective Hamiltonian expressed directly in terms of gauge invariant operators. The large N loop space constraints are handled by the use of master variables. For two and three massless Yang-Mills coupled matrices, highly accurate results for large N planar correlators, as well as spectrum, are presented. Generalization to larger number of matrices, relevant for systems such as BFSS, are discussed.

Date:
Location:
Zoom
Event Series:

String seminar

Title: Superluminal Liouville walls in 2d String Theory and space-like singularities

Abstract: An interesting class of time dependent backgrounds in 1+1 dimensional string theory involves worldsheet Liouville walls which move in (target space) time. When a parameter in such a background exceeds a certain critical value, the speed of the Liouville wall exceeds the speed of light, and there is no usual S-Matrix. We examine such backgrounds in the dual c=1 matrix model from the point of view of fluctuations of the collective field, and determine the nature of the emergent space-time perceived by these fluctuations. We show that so long as the corresponding Liouville wall remains time-like, the emergent space time is conformal to full Minkowski space with a time-like wall. However, for the cases where the Liouville wall is superluminal, the emergent space-time has a space-like boundary where the collective field couplings diverge. This appears as a space-like singularity in perturbative collective field theory. We comment on the necessity of incorporating finite $N$, as well as finite (double-scaled) coupling, effects to understand the behavior of the exact theory near this boundary.

Date:
Location:
CP 303
Event Series: