Love numbers and magnetic susceptibility of charged black holes

Abstract

The response of black holes to companions is of fundamental importance in the context of their dynamics and of gravitational-wave emission. Here, we explore the effect of charge on the static response of black holes. With a view to constraining broader setups, we consider charged geometries in an arbitrary number of spacetime dimensions $D\geq4$. Tensor tidal Love numbers are shown to follow a power law in the black hole temperature $\sim T_{H}^{2l+1}$, and thus vanish at extremality. In contrast, the black hole charge $Q$ excites new modes of polarisation in the vector sector that are otherwise not responsive in the neutral limit. In four dimensions, Love numbers and magnetic susceptibilities vanish for all values of the charge that respect the extremality bound. Using the theory of Fuchsian equations we are able to obtain analytical results in most cases, even beyond the hypergeometric instances.