String-theoretic breakdown of effective field theory near black hole horizons

TL;DR

This paper explores how string theory predicts a breakdown of the effective field theory near black hole horizons due to longitudinal string spreading, challenging the equivalence principle and suggesting new physics at horizon scales.

Contribution

It demonstrates, through light cone gauge calculations, that longitudinal string spreading can be detectable near black hole horizons, providing a potential resolution to the firewall paradox.

Findings

Detectable longitudinal string spreading near horizons

Large relative boost causes spreading despite modest energies

Implications for new physics at black hole horizons

Abstract

We investigate the validity of the equivalence principle near horizons in string theory, analyzing the breakdown of effective field theory caused by longitudinal string spreading effects. An experiment is set up where a detector is thrown into a black hole a long time after an early infalling string. Light cone gauge calculations, taken at face value, indicate a detectable level of root-mean-square longitudinal spreading of the initial string as measured by the late infaller. This results from the large relative boost between the string and detector in the near horizon region, which develops automatically despite their modest initial energies outside the black hole and the weak curvature in the geometry. We subject this scenario to basic consistency checks, using these to obtain a relatively conservative criterion for its detectability. In a companion paper, we exhibit longitudinal nonlocality in well-defined gauge-invariant S-matrix calculations, obtaining results consistent with the predicted spreading albeit not in a direct analogue of the black hole process. We discuss applications of this effect to the firewall paradox, and estimate the time and distance scales it predicts for new physics near black hole and cosmological horizons.