Absorption cross section of regular black holes in scalar-tensor conformal gravity

TL;DR

This paper analyzes the absorption cross section of regular black holes in scalar-tensor conformal gravity using complex angular momentum and WKB methods, revealing distinctive features that differentiate regular from singular black holes.

Contribution

It introduces a novel approach combining complex angular momentum and WKB methods to compute absorption cross sections of conformally related black holes, highlighting the dependence on conformal scale factors.

Findings

Absorption cross section oscillations depend on the conformal scale factor.

Regular black holes exhibit distinct absorption behavior compared to singular black holes.

The method provides a new way to distinguish regular from singular black holes.

Abstract

In terms of the complex angular momentum method, we compute the absorption cross section by analyzing a massless test scalar field around conformally related black holes. At first, we investigate circular null geodesics and thereby prove a precondition for calculating the absorption cross section in the context of conformally related black holes. Then we use the WKB approximation method to derive the analytic expression of Regge frequency and the oscillation part of absorption cross sections. We find that this oscillation part depends on the scale factor of conformal transformations. By taking the conformally related Schwarzschild-Tangherlini black hole as an example, we show that this regular black hole has substantially distinctive absorption behavior compared with singular black holes. Our result provides a new approach to distinguish a regular black hole from a singular one.