Skip to main content

String Seminar

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: 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:

Physics & Astronomy String Theory Seminar

NB: non-standard time!


Title: Symmetry-weighted ensemble averaging from TQFT gravity

Abstract: In a recently proposed framework of TQFT gravity (2310.13044, 2405.20366) -- a toy model of AdS3 gravity -- a bulk 3d TQFT summed over all topologies is shown to be dual to a unitary ensemble of boundary 2d CFTs. I will show that the CFTs in this ensemble are weighted by the inverse of the order of their symmetry group (relative to the categorical symmetry provided by the bulk TQFT as a SymTFT). Mathematically, this is the natural measure over the groupoid of the TQFT Lagrangian algebras that construct the CFTs, and the holographic duality then provides a generalization of the Siegel-Weil formula beyond averaging over bosonic lattice-CFTs. I will also discuss some examples for rational CFTs as well as implications to noncompact TQFTs and pure gravity.

Date:
-
Location:
CP 303
Event Series:

Observable projected ensembles

Most objects around us are in thermal equilibrium. But are some
systems "more thermal" than others?
The emerging paradigm of deep thermalization and projected ensembles
has indeed demonstrated that there can be
different degrees of thermality, depending on how much information can
be extracted from the system and, relatedly,
the behavior of multiple copies of the system. In my talk I will discuss a
related concept of observable projected ensembles and a
field-theoretic approach to this problem based on the replica trick.
Bases on https://arxiv.org/abs/2410.21397 and on-going work.

Date:
Location:
CP 303
Event Series:

"The evaporation of charged black holes". 

I will describe the dynamical evolution of a universe containing a single black hole. If the black hole has sufficiently large initial charge, it will be driven very close to extremality by the emission of neutral Hawking radiation, while charged particle emission is exponentially suppressed. At low enough temperatures, quantum gravity becomes important and Hawking-style quantum field theory in curved spacetime calculations give completely incorrect answers, even for simply questions like the energy spectrum of emitted radiation. This leads to interesting new physics, e.g. in certain regimes the dominant radiation channel becomes entangled pairs of photons, as in the “forbidden’’ 2s->1s hydrogen atom transition. By careful analysis of the relevant metric fluctuations, we can calculate the quantum gravity effects in a controlled manner and tell the complete story of the black hole evaporation in both a universe with a matter content similar to ours as well as in a supersymmetric universe.

Date:
Location:
CP 179
Event Series: