Bound on Lyapunov exponent for a charged particle in Kerr-Sen-AdS Black Hole

TL;DR

This paper explores the upper limits of chaos, quantified by the Lyapunov exponent, for charged particles near string-inspired black holes, revealing conditions under which the known chaos bound can be violated.

Contribution

It provides a detailed analysis of the Lyapunov exponent bounds in Kerr-Sen-AdS black holes, highlighting factors affecting potential violations in extremal regimes.

Findings

Bound sensitivity to charges, spin, and cosmological constant.

Violations occur near extremal black hole states.

Numerical results confirm analytical predictions.

Abstract

We investigate the upper bound of the Lyapunov exponent for a charged particle in the Gibbons--Maeda--Garfinkle--Horowitz--Strominger (GMGHS)--AdS and Kerr--Sen--AdS black hole backgrounds, which originate from the low-energy effective actions of heterotic string theory and gauged supergravity. We analyze the Lyapunov exponent near the unstable orbit to examine possible violations of the bound. Our results indicate that the bound is sensitive to the signs and magnitudes of the charges, the angular momentum of the particle, the black hole spin, and the negative cosmological constant. The violations are pronounced in the extremal or near-extremal regime. Numerical analysis supports the analytical predictions and highlights the interplay between the string-inspired black hole and the charged particle.