Bouncing off a stringy singularity

TL;DR

This paper explores how stringy corrections at finite coupling modify the boundary two-point function in holography, smoothing out singularities associated with black hole singularities, with evidence from the SYK model.

Contribution

It proposes a scenario where stringy effects shift boundary singularities into the complex plane, smoothing them, and demonstrates this in the SYK model at infinite temperature.

Findings

Boundary singularity is shifted into the complex plane.

Smoothing of the divergence into a finite bump observed.

Supports bulk stringy black hole interpretation at finite coupling.

Abstract

A sharp signature of the black hole singularity in holography is a divergence in the boundary thermal two-point function at a specific point in the complex time plane. This divergence arises from a null geodesic that bounces off the black hole singularity. At finite 't Hooft coupling, stringy corrections to the bulk dynamics cannot be neglected, and the fate of the bouncing geodesic is an open question. We propose a simple scenario in which the singularity in the two-point function is shifted slightly into the complex plane, thereby smoothing it out into a finite-size bump. We demonstrate this smoothing explicitly in a microscopic example, namely the Sachdev-Ye-Kitaev model at infinite temperature, where the correlator is under analytic control. Our result suggests a bulk description of planar theories at finite coupling as stringy black holes.