Eikonal quasinormal modes and shadow of string-corrected $d$-dimensional black holes

TL;DR

This paper calculates the quasinormal modes and shadow radius of string-corrected higher-dimensional black holes, revealing differences from Einstein gravity in the real parts of frequencies while the imaginary parts remain tied to null geodesics.

Contribution

It provides the first analysis of eikonal quasinormal modes and shadow properties for string-corrected $d$-dimensional black holes, highlighting deviations from classical Einstein gravity.

Findings

Real parts of quasinormal frequencies differ between tensorial and scalar perturbations.

Imaginary parts of frequencies remain equal and linked to null geodesic Lyapunov exponents.

Black hole shadow radius is computed considering string corrections.

Abstract

We compute the quasinormal frequencies of $d$-dimensional spherically symmetric black holes with leading string $\alpha'$ corrections in the eikonal limit for tensorial gravitational perturbations and scalar test fields. We find that, differently than in Einstein gravity, the real parts of the frequency are no longer equal for these two cases. The corresponding imaginary parts remain equal to the principal Lyapunov exponent corresponding to circular null geodesics, to first order in $\alpha'$. We also compute the radius of the shadow cast by these black holes.