Running Love Numbers of Charged Black Holes

TL;DR

This paper calculates the tidal response (Love numbers) of charged black holes, revealing how quantum effects and electromagnetic duality influence their deformability, with implications for gravitational-wave detection of magnetic black holes.

Contribution

It generalizes Love numbers to Love matrices for charged black holes and explores their quantum and electromagnetic duality properties, extending previous work to include magnetic black holes.

Findings

Love matrices relate to U(1) gauge coupling running.

Quantum corrections break electromagnetic duality.

Magnetic black holes' tidal response saturates in strong fields.

Abstract

Loops of virtual particles from the vacuum of quantum field theory (QFT) render black holes tidally deformable. We compute the static tidal response of unspinning charged black holes at arbitrary radius, using the perturbative formalism developed in 2501.18684. Since the gravitational and electromagnetic tidal responses mix, we generalize the notion of Love numbers to Love matrices. We derive the coupled equations of motion for the metric and electromagnetic fluctuations around purely electric and magnetic backgrounds. For large charged black holes, which are described by the Effective Field Theory (EFT) of gravity, we compute the full set of Love matrices induced by an arbitrary tower of $F^{2n}$ operators. We find that, although quantum corrections break electromagnetic duality, the Love matrices in electric and magnetic backgrounds are related by a $Z_2$ symmetry under electric-magnetic exchange. Going beyond EFT, we compute the Love matrices of small magnetic black holes. We show that the running of the Love matrices is governed by the running of the $U(1)$ gauge coupling, and we derive the correspondence between Love and $U(1)$ beta functions for arbitrary harmonics. The overall picture that emerges is that the QFT-induced tidal response of magnetic black holes saturates in the strong-field regime. These results imply that nearly-extremal magnetic black holes charged under an Abelian dark sector could be probed by gravitational-wave observations.