Quantum-corrected ultraextremal horizons and validity of WKB in massless limit

TL;DR

This paper investigates quantum backreaction effects on ultraextremal horizons, demonstrating the validity of the WKB approximation in the massless limit and confirming the existence of quantum-corrected solutions.

Contribution

It shows that the WKB approximation remains valid near ultraextremal horizons even for massless fields, extending previous results to this special case.

Findings

Quantum-corrected ultraextremal horizons exist.

WKB approximation remains valid in the massless limit.

Results agree with large mass limit previous studies.

Abstract

We consider quantum backreaction of the quantized scalar field with an arbitrary mass and curvature coupling on ultraextremal horizons. The problem is distinguished in that (in contrast to non-extremal or extremal black holes) the WKB approximation remains valid near $r_{+}$ (which is the radius of the horizon) even in the massless limit. We examine the behavior of the stress-energy tensor of the quantized field near $r_{+}$ and show that quantum-corrected objects under discussion do exist. In the limit of the large mass our results agree with previous ones known in literature.