Dark energy radiation
Kim V. Berghaus, Peter W. Graham, David E. Kaplan, Guy D. Moore, Surjeet Rajendran
Abstract
We show that if dark energy evolves in time, its dynamical component could be dominated by a bath of dark radiation. Within current constraints this radiation could have up to $\ensuremath{\sim}{10}^{3}$ times more energy density than the cosmic microwave background. We demonstrate particular models in which a rolling scalar field generates different forms of dark radiation such as hidden photons, millicharged particles, and even Standard Model neutrinos. We find the leading effect on the late-time cosmological expansion history depends on a single parameter beyond the standard cosmological model, namely the temperature of the dark radiation today. Cosmological observations of this modified expansion rate could provide a striking signature of this scenario. The dark radiation itself could even be directly detectable in laboratory experiments, suggesting a broader experimental program into the nature of dark energy.