Shedding black hole light on the emergent string conjecture

TL;DR

This paper investigates the relationship between towers of light species and small black holes in quantum gravity, providing bottom-up constraints that support the emergent string conjecture without relying on specific ultraviolet completions.

Contribution

It introduces a novel bottom-up approach to constrain light species towers using black hole thermodynamics, supporting the emergent string conjecture.

Findings

Constraints on light species towers consistent with black hole thermodynamics.

Evidence supporting the emergent string scenario from unitarity and causality.

Insights into allowed towers in quantum gravity.

Abstract

Asymptotically massless towers of species are ubiquitous in the string landscape when infinite-distance limits are approached. Due to the remarkable properties of string dualities, they always comprise Kaluza-Klein states or higher-spin excitations of weakly coupled, asymptotically tensionless critical strings. The connection between towers of light species and small black holes warrants seeking a bottom-up rationale for this dichotomoy, dubbed emergent string conjecture. In this paper we move a first step in this direction, exploring bottom-up constraints on towers of light species motivated purely from the consistency of the corresponding thermodynamic picture for small black holes. These constraints shed light on the allowed towers in quantum gravity, and, upon combining them with unitarity and causality constraints from perturbative graviton scattering, they provide evidence for the emergent string scenario with no reference to a specific ultraviolet completion.