Matrix elements of four-quark operators and ΔL = 2 hyperon decays

Abstract

The study of neutrinoless double beta decays of nuclei and hyperons requires the calculation of hadronic matrix elements of local four-quark operators that change the total charge by two units ΔQ = 2. Using a low energy effective Lagrangian that induces these transitions, we compute these hadronic matrix elements in the framework of the Massachussetts Institute of Technology bag model. As an illustrative example we evaluate the amplitude and transition rate of ε- → pe-e-, a decay process that violates lepton number by two units (ΔL = 2). The relevant matrix element is evaluated without assuming the usual factorization approximation of the four-quark operators and the results obtained in both approaches are compared.