Seminar of the department “Theory of Fundamental Interactions”

Date and Time: Thursday, 15 October 2020, at 4:00 PM

Venue: Online conference in Zoom, Bogoliubov Laboratory of Theoretical Physics

Seminar topic: «Neutrino mass, double-beta decay and nuclear structure»

Speaker: Fedor Simkovic

Abstract:

A Quark Condensate See-Saw mechanism of generation of Majorana neutrino mass due to spontaneous breaking of chiral symmetry accompanied with the formation of a quark condensate is presented. Consequences of this scenario of neutrino mass generation for the neutrinoless double beta decay (0𝜈𝛽𝛽-decay), tritium beta decay and cosmological measurements are drawn. The question is addressed whether light and heavy neutrino contributions to 0𝜈𝛽𝛽-decay are experimentally distinguishable. In that context, the “interpolating formula” for the 0nbb-decay is revisited. Several simplified benchmark scenarios within left-right symmetric models are considered and the conditions for the dominance of the light or heavy neutrino mass mechanisms are analyzed. A 6 x 6 unitary matrix for parameterizing the mixing among three flavours of the quasi-Dirac neutrino is proposed. This mixing matrix is constructed by two 3 x 3 unitary matrices that diagonalizes the Dirac mass term in the Lagrangian. Consequences for neutrino oscillations and 0𝜈𝛽𝛽-decay are drawn. The attention is paid also to the problem of reliable calculation of the 0𝜈𝛽𝛽-decay nuclear matrix elements. The progress achieved within the QRPA approach is presented. A connection between the 2𝜈𝛽𝛽-decay and 0𝜈𝛽𝛽-decay matrix elements are analyzed. An impact of the quenching of the axial-vector coupling constant on double-beta decay processes is investigated and a novel approach to determine the quenched value of the axial-vector coupling constant is proposed. For reliable determination of the 0𝜈𝛽𝛽-decay nuclear matrix elements importance of the experimental study of the 2𝜈𝛽𝛽-decay, muon capture in nuclei and nuclear charge-exchange reactions is stressed. The calculation of the muon capture rate within the QRPA approach for double-beta decaying isotopes is revisited.

(in connection with the nomination for the JINR award)