# Quasinormal modes and absorption cross sections of Born-Infeld-de Sitter black holes

## TL;DR

This study investigates the quasinormal modes and absorption cross sections of Born-Infeld-de Sitter black holes using WKB and null geodesic methods, comparing nonlinear electromagnetic effects with linear cases.

## Contribution

It introduces a combined approach using WKB and null geodesics to analyze QNMs and absorption cross sections of Born-Infeld-de Sitter black holes, highlighting nonlinear electromagnetic influences.

## Key findings

- QNMs computed via WKB and eikonal approximation agree in the high-frequency limit.
- Unstable null geodesics determine QNM frequencies in the eikonal regime.
- Absorption cross sections are estimated using the sinc approximation at high frequencies.

## Abstract

In this paper, we have studied QNM modes and absorption cross sections of Born-Infeld-de Sitter black holes. WKB approximation is employed to compute the QNM modes of massless scalar fields. We have also used null geodesics to compute quasi-normal modes in the eikonal approximation. In the eikonal limit QNMs of black holes are determined by the parameters of the circular null geodesics. Unstable circular null orbits are derived from the effective metric which is obeyed by light rays under the influence of a nonlinear electromagnetic field. Comparison is shown with the QNM of the linear electromagnetic counterpart, the Reissner-Nordstr\"{o}m black hole. Furthermore, the null geodesics are employed to compute the absorption cross sections in the high frequency limit via the sinc approximation.