Abstract:

Neutrinos are truly unique particles for investigating the matter of nuclei as well as that of distant astrophysical objects in our Universe. We still do not know some of neutrino fundamental properties like their mass or whether neutrinos are their own antiparticles. Answering these questions is the subject of experimental investigations.

The first part of the talk will be devoted to theoretical calculations, the second one — to experimental observations.

To date, the method based on measurement of the energy spectrum of electrons in beta decays of tritium and other particles has the highest sensitivity to neutrino mass determination. The KATRIN (MARE2) experiment is based on this method. A highly accurate theoretical description of the electron energy spectrum near the endpoint is crucial for this task. The shape of the tritium and rhenium beta spectrum will be presented during this talk. Conclusions on the shape close to the endpoint arising from the exact relativistic treatment of the tritium beta decay will be highlighted.

Experimental observation of the neutrinoless double-beta decay will manifest the Majorana nature of neutrinos. The 0nbb-decay rate is factorized as a sum of products involving nuclear matrix elements and kinematical phase-space factors. Improvement of numerical calculation of phase-space factors, angular distribution and single electron energy spectra, the effect of quenching of the axial-vector coupling constant will be discussed.

Baikal-GVD is a neutrino telescope aimed at high-energy neutrino detection. The telescope is a three-dimensional array of photosensors installed in Lake Baikal. Apart from Cherenkov light related to relativistic particles, the ambient light of the lake is also registered. Some selected results on lake luminescence will be presented and discussed during this talk as well.

(In connection with the election to fill the position of a senior researcher).