Topological deformation of isolated horizons

TL;DR

This paper demonstrates that the Gauss-Bonnet term influences black hole entropy in four dimensions, especially during dynamical topological changes like mergers, potentially violating the second law of black-hole mechanics.

Contribution

It reveals the physical effects of the Gauss-Bonnet term on black hole entropy and topological dynamics in four-dimensional spacetime.

Findings

Gauss-Bonnet term affects black hole entropy in 4D.

Entropy correction is proportional to horizon's Euler characteristic.

Second law can be violated during dynamical topological changes.

Abstract

We show that the Gauss-Bonnet term can have physical effects in four dimensions. Specifically, the entropy of a black hole acquires a correction that is proportional to the Euler characteristic of the cross sections of the horizon. While this term is constant for a single black hole, it will be a non-trivial function for a system with dynamical topologies such as black-hole mergers: it is shown that for certain values of the GB parameter, the second law of black-hole mechanics can be violated.