Charged black-hole binary radiation at second post-Newtonian order

Abstract

In this work, we build on Ref.~[Phys.~Rev.~D 112, 124060 (2025)], where we derived the dynamics of an electrically charged binary system at second post-Newtonian (2PN) order, by extending the analysis, at the same PN accuracy, to the associated emission of electromagnetic and gravitational radiation. We focus on non-spinning binaries that evolve quasi-adiabatically along a sequence of circular orbits, and compute the 2PN expression for the corresponding total energy flux at infinity. With respect to the well-known case of a neutral binary, the presence of charge induces both a new leading-order electromagnetic contribution of dipolar nature and additional charge-dependent corrections in the gravitational sector. To account for this richer phenomenology, we extend both the PN-matched multipolar post-Minkowskian and the effective field theory approaches to the radiation sector of charged binaries, with exact agreement for the contributions computed independently in both formalisms. We derive the radiative symmetric-trace-free multipole moments of the vector and gravitational fields at 2PN order. In doing so, we also compute 2PN-accurate charge-dependent corrections to the spherical multipoles of the waveform emitted by the binary, including a new memory contribution sourced by the stress-energy tensor of the electromagnetic radiation. These results lay the foundation for developing accurate waveform models capable of assessing the observational signatures of electric charge in gravitational-wave signals.