Abstract
In viable models of minicharged dark matter, astrophysical black holes might be charged under a hidden U(1) symmetry and are formally described by the same Kerr-Newman solution of Einstein-Maxwell theory. These objects are unique probes of minicharged dark matter and dark photons. We show that the recent gravitational-wave detection of a binary black-hole coalescence by aLIGO provides various observational bounds on the black hole's charge, regardless of its nature. The pre-merger inspiral phase can be used to constrain the dipolar emission of (ordinary and dark) photons, whereas the detection of the quasinormal modes set an upper limit on the final black hole's charge. By using a toy model of a point charge plunging into a Reissner-Nordstrom black hole, we also show that in dynamical processes the (hidden) electromagnetic quasinormal modes of the final object are excited to considerable amplitude in the gravitational-wave spectrum only when the black hole is nearly extremal. The coalescence produces a burst of low-frequency dark photons which might provide a possible electromagnetic counterpart to black-hole mergers in these scenarios.
Highlights
Charge but interact among each other only through the exchange of dark photons, the latter being the mediators of a long-range gauge interaction with no coupling to Standard-Model particles [23]
In viable models of minicharged dark matter, astrophysical black holes might be charged under a hidden U (1) symmetry and are formally described by the same Kerr-Newman solution of Einstein-Maxwell theory
By using a toy model of a point charge plunging into a Reissner-Nordstrom black hole, we show that in dynamical processes the electromagnetic quasinormal modes of the final object are excited to considerable amplitude in the gravitational-wave spectrum only when the black hole is nearly extremal
Summary
Where Fμν := ∂μAν − ∂νAμ and Bμν := ∂μBν − ∂νBμ are the field strengths of the ordinary photon and of the dark photon, respectively, jeμm and jhμ are the electromagnetic (EM) and the hidden number currents, e is the electron charge, and eh is the gauge coupling of the hidden sector. Observational bounds on minicharged DM typically constrain the coupling to Standard-Model particles, especially the coupling to ordinary photons. As such, they are insensitive to the coupling eh which is typically neglected.
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