Abstract
We present a mechanism for generating ultralight dark photon dark matter in
the early Universe via a dilatonlike scalar field coupled to the dark photon's
kinetic term. Energy is initially stored in the condensate of the dilaton,
which resonantly produces dark photons when it begins oscillating in the early
Universe. While similar scenarios with axion--dark-photon couplings require
large coupling coefficients to fully populate the dark photon, the dilatonic
coupling features a unique regime: when the dark photon's mass is half that of
the dilaton, dark photons are copiously produced even when the dilaton
undergoes small-amplitude oscillations. Scenarios consistent with the cosmic
microwave background allow for ultralight vector dark matter with mass as light
as $10^-20$ eV.
Users
Please
log in to take part in the discussion (add own reviews or comments).