Self-interacting fundamental strings and black holes

TL;DR

This paper rigorously analyzes the size distribution of massive string states and their transition to black holes, confirming that at the black hole/string transition, strings are confined within the horizon scale.

Contribution

It provides a rigorous string theory computation of string state sizes and their relation to black hole horizons, clarifying previous approximation-based results.

Findings

String states are dominated by compact configurations within the black hole horizon.

The transition point aligns with the black hole correspondence principle.

String size at transition is of the order of the string scale.

Abstract

We study the size distribution of very massive close string states and the typical string configuration as one slowly increase the string coupling, both in the case of zero and of non-zero Neveu-Schwarz charges. The computations are performed rigorously in string theory, starting from quantities that are well-defined in the theory and therefore clarify previous works on the subject which were based on various approximation techniques. We find that, starting from a value of the coupling in agreement with the one predicted by the black hole correspondence principle, the string ensemble is dominated in any dimensions by compact states whose size is within the correspondent black hole horizon radius, which is of the order of the string scale at the black hole/string transition point.