Theory of double beta decay

Basic features of the two-neutrino double beta (2νββ) decay and neutrinoless double beta (0νββ) decay are discussed. A short review of the most important nuclear models, used to describe the ββ decay, is given. A deeper survey of the nuclear matrix elements, related to the above-mentioned decay modes, is performed using the proton-neutron quasiparticle random-phase approximation (pnQRPA). In particular, the extraction of a proper value of the proton-neutron particle-particle interaction parameter in this theory is addressed. The relevance of different multipoles in the multipole decomposition of the 0νββ matrix element is also discussed in the pnQRPA framework.