The Simons Center for Geometry and Physics is pleased to announce the following talks during the week of Monday, April 27th - Saturday, May 2nd

Program Talk: Hao Geng

Monday, April 27th at 11:15am in SCGP 313

Speaker: Hao Geng

Title: It From ETH Part II

Abstract: In this talk, I will recap what we discussed in the workshop and finish the rest of it. I'll explain how the Cardy boundary enriched large-c CFT ensemble enbles a derivation of the multi-intervel entanglement entropy in AdS3/CFT2 and provides a natural way to see the emergence of the replica wormhole in the calculation of the Page curve of the black hole radiation. I'll also discuss some open problems in quantum gravity inspired by our work.

Program Talk: Masamichi Miyaji

Monday, April 27th at 2:00pm in SCGP 313

Speaker: Masamichi Miyaji

Title: Perturbative Hilbert space of JT closed universes

Abstract: We consider gravitational path-integral of JT gravity of closed universe in AdS and dS spacetimes, for fixed extrinsic curvature boundary conditions where the spacetime boundary is rigid rather than random. In the absence of topology change, we calculate the amplitude and identify the perturbative Hilbert space. We find the Hilbert space is given by the infinite-dimensional co-invariant Hilbert space, which can be obtained from a space of boundary conditions modded by constraints. We also propose a finite N regularization of the model, whose Hilbert space dimension is non-trivial.

Physics Seminar: Noa Zilberman

Wednesday, April 29th at 2:00pm in 313

Title: The quantum energy outflux emerging from a collapsing shell    

Abstract: When a compact object collapses to form a black hole, quantum field theory predicts the emission of an energy outflux to future null infinity, which later relaxes to Hawking radiation. Within the semiclassical framework, we derive a simple, closed form, analytical expression for the energy outflux emitted from a spherical thin null shell collapsing to form a black hole. In particular, this energy outflux vanishes (quadratically in r-2M) as the shell approaches the horizon. This result refutes claims that the Hawking energy outflux originates from the collapsing body, showing instead that it develops in a broad strong-field region. Additionally, this vanishing implies that semiclassical backreaction cannot prevent or significantly affect the classical process of gravitational collapse and horizon formation (as sometimes claimed). This talk is based on the joint work arXiv:2503.00622 with Amos Ori.