Double-beta decay and its potential to explore beyond standard model physics

Abstract

Double-beta decay (DBD) is a rare nuclear process of great interest due to its potential to provide information about physics beyond the Standard Model (BSM). For example, the discovery of the neutrinoless double-beta [Formula: see text] decay mode could give information about important issues such as possible violations of Lorentz symmetry and lepton number, nature of neutrinos (are they Dirac- or Majorana-like particles?), neutrino absolute masses, neutrino mass hierarchy, existence of heavy (sterile) neutrinos, etc. In the theoretical study of DBD, one needs a precise calculation of the nuclear matrix elements (NMEs) and phase space factors (PSFs) entering the half-lives formulas, for different decay modes, transitions and mechanisms of occurrence. Reliable computations of these quantities may result in reliable predictions of DBD half-lives and constrains of the BSM parameters related to the possible mechanisms that can contribute to the [Formula: see text] decay. In this paper, I briefly review the theoretical challenges in the study of [Formula: see text] decay. I describe the computation of the NMEs and PSFs and present results for a number of selected nuclei. Then, I show the broader potential of this process to provide information about BSM physics and present new upper limits for parameters associated with light neutrino, heavy neutrino and SUSY exchange mechanisms. Finally, I suggest a more consistent approach to calculate the NMEs and PSFs, namely to compute directly their product and discuss some possibilities to reduce the errors related to the uncertain value of the axial-vector constant.