Hairy binary black holes in Einstein-Maxwell-dilaton theory and their effective-one-body description

Abstract

In General Relativity and many modified theories of gravity, isolated black holes (BHs) cannot source massless scalar fields. Einstein-Maxwell-dilaton (EMd) theory is an exception: through couplings both to electromagnetism and (non-minimally) to gravity, a massless scalar field can be generated by an electrically charged BH. In this work, we analytically model the dynamics of binaries comprised of such scalar-charged ("hairy") BHs. While BHs are not expected to have substantial electric charge within the Standard Model of particle physics, nearly-extremally charged BHs could occur in models of minicharged dark matter and dark photons. We begin by studying the test-body limit for a binary BH in EMd theory, and we argue that only very compact binaries of nearlyextremally charged BHs can manifest non-perturbative phenomena similar to those found in certain scalar-tensor theories. Then, we use the post-Newtonian approximation to study the dynamics of binary BHs with arbitrary mass ratios. We derive the equations governing the conservative and dissipative sectors of the dynamics at next-to-leading order, use our results to compute the Fourierdomain gravitational waveform in the stationary-phase approximation, and compute the number of useful cycles measurable by the Advanced LIGO detector. Finally, we construct two effective-onebody (EOB) Hamiltonians for binary BHs in EMd theory: one that reproduces the exact test-body limit and another whose construction more closely resembles similar models in General Relativity, and thus could be more easily integrated into existing EOB waveform models used in the data analysis of gravitational-wave events by the LIGO and Virgo collaborations.

Gravitational radiation from compact binary systems in Einstein-Maxwell-dilaton theories

“…When α 0 A = α 0 B , this flux is reduced to its purely (scalar) quadrupolar term. This expression generalizes that of Damour and Esposito-Farèse in scalar-tensor theories [9], which is recovered when e A/B = 0; note however that the EMD flux cannot be deduced from [9] by a mere generalization of G AB to include e A/B , due to the presence of a in the last term of (14).…”

“…Having in hand the fluxes (12)(13)(14), one can also deduce the radiation reaction force exerted on the system by equating its power to the energy fluxes at infinity [10]. For the quasi-circular orbits considered here, this force is tangent to the trajectory and reads…”

Post-Newtonian dynamics and black hole thermodynamics in Einstein-scalar-Gauss-Bonnet gravity

“…(IV.9)], yield the full EsGB Lagrangian at 3PN order. It will be interesting to extend the effectiveone-body program to this more general class of theories: see [69,70] for similar work in "ordinary" scalar-tensor gravity, and [28,49] for related work in EMD theory.…”

Eikonal scattering in Kaluza-Klein gravity

“…There has been recent interest in investigating binary black hole systems in the post-Minkowskian approximation [25,26] as these results could provide useful theoretical modelling of gravitational waves detected by LIGO [27]. Recent work [28] has investigated the particular case of binary Einstein-Maxwell-dilaton black holes in the post-Newtonian approximation. We believe that our result for the eikonal in Kaluza-Klein theories,…”