Dark energy radiation

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