Neutrinoless double β decay with light sterile neutrinos: the contact terms

A bstract We study neutrinoless double-beta decay in extensions of the Standard Model that include n right-handed neutrino singlets, with masses m s below the GeV scale. Generalizing recently developed matching methods, we determine the m s dependence of the short-range nn → pp couplings that appear to leading order in the chiral effective field theory description of neutrinoless double beta decay. We focus on two scenarios, corresponding to the minimal ν SM and left-right symmetric models. We illustrate the impact of our new results in the case of the ν SM, showing a significant impact on the neutrinoless double-beta decay half-life when m s is in the 200–800 MeV range.