# On the black hole interior in string theoy

## TL;DR

This paper explores the structure behind black hole horizons in string theory, revealing that non-perturbative effects suggest a complex region just behind the horizon, contrasting with classical expectations.

## Contribution

It analyzes the reflection coefficient in string theory black holes, showing non-perturbative effects imply a non-trivial structure behind the horizon.

## Key findings

- Reflection coefficient indicates complex horizon structure
- Non-perturbative effects alter classical horizon picture
- Potential is regular at horizon but complex behind it

## Abstract

The potential behind the horizon of an eternal black hole in classical theories is described in terms of data that is available to an external observer -- the reflection coefficient of a wave that scatters on the black hole. In GR and perturbative string theory (in $\alpha'$), the potential is regular at the horizon and it blows up at the singularity. The exact reflection coefficient, that is known for the $SL(2,\mathbb{R})_k/U(1)$ black hole and includes non-perturbative $\alpha'$ effects, seems however to imply that there is a highly non-trivial structure just behind the horizon.