Towards a superformula for neutrinoless double beta decay

Abstract

A general Lorentz--invariant parameterization for the long-range part of the $0νββ$ decay rate is derived. Combined with the short range part this general parameterization in terms of effective $B-L$ violating couplings will allow it to extract the $0νββ$ limits on arbitrary lepton number violating theories. Several new nuclear matrix elements appear in the general formalism compared to the standard neutrino mass mechanism. Some of these new matrix elements have never been considered before and are calculated within pn-QRPA. Using these, limits on lepton number violating parameters are derived from experimental data on $^{76}$Ge.