Neutrino meets ultralight dark matter: 0νββ decay and cosmology

Abstract

We explore the neutrinoless double beta (0νββ) decay induced by an ultralight dark matter field coupled to neutrinos. The effect on 0νββ decay is significant if the coupling violates the lepton number, for which the ΔL = 2 transition is directly driven by the dark matter field without further suppression of small neutrino masses. As the ultralight dark matter can be well described by a classical field, the effect features a periodic modulation pattern in decay events. However, we find that in the early Universe such coupling will be very likely to alter the standard cosmological results. In particular, the requirement of neutrino free-streaming before the matter-radiation equality severely constrains the parameter space, such that the future 0νββ decay experiments can hardly see any signal even with a meV sensitivity to the effective neutrino mass.