Mirror effect induced by the dilaton field on the Hawking radiation

TL;DR

This paper explores how a dilaton-induced mirror surface near an extremal black string affects Hawking radiation, potentially halting evaporation before a naked singularity forms.

Contribution

It introduces a dilaton-induced mirror effect that alters string creation and black string evaporation in non-critical string models.

Findings

Dilaton field creates a timelike mirror surface outside the horizon.

Reflection of strings prevents negative energy flux from crossing the surface.

Black string evaporation halts before naked singularity formation.

Abstract

We discuss the string creation in the near-extremal NS1 black string solution. The string creation is described by an effective field equation derived from a fundamental string action coupled to the dilaton field in a conformally invariant manner. In the non-critical string model the dilaton field causes a timelike mirror surface outside the horizon when the size of the black string is comparable to the Planck scale. Since the fundamental strings are reflected by the mirror surface, the negative energy flux does not propagate across the surface. This means that the evaporation stops just before the naked singularity of the extremal black string appears even though the surface gravity is non-zero in the extremal limit.