Stringy resolution of bouncing singularities

Abstract: We study the near-horizon geometry of near-extremal NS5 branes, which admits an exact worldsheet description in terms of the $SL(2,\mathbb{R})_k/U(1)$ coset. In the supergravity limit, the analytically continued time-domain reflection amplitude exhibits a singularity associated with a null geodesic bouncing off the black-hole singularity, analogous to the bouncing singularities of boundary correlators in asymptotically AdS spacetimes. We show that finite-string-length effects render this amplitude an entire function of complex time, completely resolving the bouncing singularity. This resolution is nonperturbative in the inverse coset level: the singularity persists at every finite order in the expansion.