Blandford-Znajek Process in Quadratic Gravity

TL;DR

This paper explores how quadratic gravity theories, specifically scalar Gauss-Bonnet and dynamical Chern-Simons gravity, affect the energy extraction process from rotating black holes, revealing modifications to the Blandford-Znajek mechanism.

Contribution

It provides analytical solutions for the Blandford-Znajek process in quadratic gravity theories, highlighting how these theories alter energy extraction compared to general relativity.

Findings

Power is enhanced in scalar Gauss-Bonnet gravity.

Power is reduced in dynamical Chern-Simons gravity.

Degeneracy between spin and coupling constants is broken at higher orders.

Abstract

The Blandford-Znajek process, which uses a magnetized plasma to extract energy from a rotating black hole, is one of the leading candidates for powering relativistic jets. In this work, we investigate the Blandford-Znajek process in two well-motivated quadratic gravity theories: scalar Gauss-Bonnet and dynamical Chern-Simons gravity. We solve analytically for a split-monopole magnetosphere to first order in the small-coupling approximation and second relative order in the slow-rotation approximation. The extracted power at fixed spin and magnetic flux is enhanced in scalar Gauss-Bonnet and reduced in dynamical Chern-Simons gravity, compared to general relativity. We find that there is a degeneracy between spin and the coupling constants of the theories at leading order in the slow rotation approximation that is broken at higher orders.