Alejandro Cabo-Bizet  博士学术报告

Title: Why Indices Count the Total Number of Black Hole Microstates (at large N)

Speaker: Alejandro Cabo-Bizet

Affiliation: University of Turin, Italy（意大利都灵大学）

Time: 16:00-17:00, Friday, March 27th, 2026 (UTC+8, Beijing Time)

Venue: Zoom Meeting (ID: 385 442 0225; Passcode: yauc)

Inviter: Ryo Suzuki

Slides_ Why Indices Count the Total Number of Black Hole Microstates (at large N)_CaboBizet.pdf

Abstract

Understanding why Witten indices reproduce the exponential of the Bekenstein--Hawking entropy of supersymmetric black holes—despite counting bosonic and fermionic states with opposite signs—has remained a long-standing puzzle in string theory and gauge/gravity duality.

In this talk we will address this question in the canonical example of the duality between four-dimensional maximally supersymmetric Yang--Mills theory and ten-dimensional Type IIB supergravity/string theory. Concretely, we will explain why the superconformal index of this gauge theory, after averaging out oscillations, reproduces the semiclassical entropy of the dual supersymmetric black holes in the relevant asymptotic expansions. As a by-product, we will provide a microscopic interpretation of a non-linear constraint among charges that is well known to correspond, on the gravitational side of the duality, to the absence of naked CTCs in the Lorentzian black hole geometry.

Our results indicate that, rather than the superconformal index, the natural observable for counting black-hole microstates at finite $N$ is the Boltzmann partition function over BPS states. The talk will be based on 2512.19946 and on ongoing work.

Speaker

Alejandro Cabo Bizet obtained his PhD from SISSA and held postdoctoral positions at ICTP (Trieste), IAFE (Buenos Aires), King’s College London, and INFN (Lecce). He is currently a postdoctoral researcher at INFN, University of Turin.

The seminar will be broadcasted online by Zoom.

Interested people are free to join, without registration in advance.

The Zoom info is

URL: https://us02web.zoom.us/j/3854420225?pwd=SXY4eWJKOTBFZWJDaE16aXpTamY1QT09

Meeting ID: 385 442 0225

Passcode: yauc