From Fundamental Strings to Small Black Holes

TL;DR

This paper provides evidence for a transition from fundamental strings to small black holes in heterotic string theory, analyzing the evolution of dynamical quantities and absorption cross sections across the transition.

Contribution

It offers a detailed analysis of the string/black hole transition, including dynamical evolution and cross section calculations, extending beyond simple state counting.

Findings

String states shrink to the string scale before black hole formation

Absorption cross sections serve as order parameters for the transition

Cross sections for horizon-fixed scalars approach zero at black hole formation

Abstract

We give evidence in favour of a string/black hole transition in the case of BPS fundamental string states of the Heterotic string. Our analysis goes beyond the counting of degrees of freedom and considers the evolution of dynamical quantities in the process. As the coupling increases, the string states decrease their size up to the string scale when a small black hole is formed. We compute the absorption cross section for several fields in both the black hole and the perturbative string phases. At zero frequency, these cross sections can be seen as order parameters for the transition. In particular, for the scalars fixed at the horizon the cross section evolves to zero when the black hole is formed.