Please contact erule@berkeley.edu for zoom links.

If dark energy evolves in time its dynamical component could be dominated by a bath of dark radiation. Since dark energy was subdominant in the early universe, the dark energy radiation evades the usual stringent constraints on extra relativistic species from the cosmic microwave background, allowing for up to 9% of the energy density today to be dark radiation. In this talk, I will discuss how dark energy radiation can emerge from a fundamental theory, its predictions for cosmological observables, as well as discovery potential and constraints with existing and future precision cosmological datasets including measurements of the cosmic microwave background, baryon acoustic oscillations, and supernova data. Considering extensions that allow the dark radiation to populate neutrinos, axions, and dark photons, I will discuss the direct detection prospects of a thermal background comprised of these candidates consistent with cosmological constraints on dark energy radiation. A dark photon background is the most promising prospect for direct detection, and experimental programs such as the late dark energy radiation experiment (LADERA) will probe new parameter space.