String Seminar

String seminar

Title: Non-perturbative structure from invariant theory

Abstract: At finite N the ring of gauge invariant operators is not freely generated. However, the full invariant ring is a free module over a polynomial ring generated by the primary invariants. The module basis is given by finitely many secondary invariants. This motivates a physical picture in which the primary invariants are regarded as perturbative degrees of freedom while the secondary invariants are associated with distinguished non-perturbative states or sectors. This talk will show that a concrete algebraic version of this picture is already visible in simple zero-dimensional matrix integrals.

Date:
Location:
CP 303
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String seminar

Note unusual location and time!

Title: The Stretched Horizon

Abstract: We will study the theory of general relativity in the presence of a timelike boundary that is parametrically close to a (non-degenerate) event horizon. We will focus on the case where the boundary is subject to conformal boundary conditions in which the conformal class of the metric and the trace of the extrinsic curvature are kept fixed at the boundary. At the linearised level, we will show the existence of soft and fluid-like modes, which are indicative of certain local structure at the boundary.
 

Date:
Location:
CP 179
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String Seminar

Title: Single-Sided Black Holes in Double-Scaled SYK Model and No Man's Island
 
Abstract: We study a single-sided black hole with an end-of-the-world (EoW) brane behind the horizon in the double-scaled SYK (DSSYK). The new Hamiltonian is a deformation of the original DSSYK Hamiltonian with an extra exponential wormhole length operator, which leads to a new chord diagram rule. The boundary algebra is defined as generated by the new Hamiltonian and boundary matter. 
 
There is an alternative but equivalent definition with a q-coherent state due to a nontrivial isomorphism of the vN algebra of DSSYK. This isomorphism induces a unitary equivalence, which yields a surprising result that the boundary algebra of a single-sided black hole in DSSYK has a non-trivial commutant and is a type II1 vN factor. It follows that the full bulk reconstruction from the boundary is impossible, and there is a "no man's island" behind the horizon in the semiclassical JT limit. Inspired by the EoW brane, we construct a family of matter-brane states with an arbitrary number of matter chords and behaving like an EoW brane. They exactly solve the full spectrum of DSSYK.

We take different ways to understand the nontrivial commutant. We show that the commutant is complex on chord number basis and thus non-geometric. In the semiclassical JT limit, the commutant becomes the canonical purification of the boundary algebra and claims the no man's island. In the context of Hawking radiation after Page time, the unitary equivalence is interpreted as encoding the canonical purification into the old Hawking radiation and the no man's island has the same essence as the island. 
 
Including the exponential wormhole length operator independently, the boundary algebra is extended to all bounded operators and reconstructs the no man's island. This can be regarded as a different choice for the definition of boundary algebra. This type I∞ algebra is closely related to the EoW brane in Kourkoulou-Maldacena.
Date:
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Location:
CP 303
Event Series:

String Seminar

Title:
The Gravitational Path Integral and Axion Wormholes

Abstract:
We investigate the relevance of axiom wormholes to the AdS/CFT factorization problem using Lorentz-signature gravitational path integrals.

Zoom Link
 

Date:
Location:
Zoom
Event Series:

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: