Oscillations in the electron-capture (EC) decay rate observed in storage-ring experiments are reconsidered in connection with the neutrino mass difference. Taking into account that - according to Relativity Theory - time is slowed down in the referen
ce frame of the orbiting charged particles as compared to the neutral particles (neutrinos) moving on a rectilinear path after the EC decay, we derive a value of $Delta m^{2}_{21}=(0.768pm0.012)cdot10^{-4} eV^{2}$ for the neutrino mass-squared difference which fully agrees with that observed in other neutrino-oscillation experiments. To further check the connection between EC-decay oscillations and $Delta m^{2}_{21}$ we suggest experiments with different orbital speeds, i.e., different values of the Lorentz factor.
From the standard seesaw mechanism of neutrino mass generation, which is based on the assumption that the lepton number is violated at a large (~10exp(+15) GeV) scale, follows that the neutrinoless double-beta decay is ruled by the Majorana neutrino
mass mechanism. Within this notion, for the inverted neutrino-mass hierarchy we derive allowed ranges of half-lives of the neutrinoless double-beta decay for nuclei of experimental interest with different sets of nuclear matrix elements. The present-day results of the calculation of the neutrinoless double-beta decay nuclear matrix elements are briefly discussed. We argue that if neutrinoless double-beta decay will be observed in future experiments sensitive to the effective Majorana mass in the inverted mass hierarchy region, a comparison of the derived ranges with measured half-lives will allow us to probe the standard seesaw mechanism assuming that future cosmological data will establish the sum of neutrino masses to be about 0.2 eV.
Basic questions concerning phononless resonant capture of monoenergetic electron antineutrinos (Mossbauer antineutrinos) emitted in bound-state beta-decay in the 3H - 3He system are discussed. It is shown that lattice expansion and contraction after
the transformation of the nucleus will drastically reduce the probability of phononless transitions and that various solid-state effects will cause large line broadening. As a possible alternative, the rare-earth system 163Ho - 163Dy is favoured. Mossbauer-antineutrino experiments could be used to gain new and deep insights into several basic problems in neutrino physics.
Basic aspects of phononless resonant capture of monoenergetic electron antineutrinos (Moessbauer antineutrinos) emitted in boundstate beta-decay in the 3H - 3He system are considered. It is shown that stochastic magnetic relaxation phenomena as well
as the direct influence of solid-state effects on the energy of the electron antineutrino will cause line broadening by a factor of more than 10^(13). Lattice expansion and contraction after the transformation of the nucleus will drastically reduce the probability for phononless transitions. Thus, the observation of Moessbauer electron antineutrinos of the 3H - 3He system will most probably be unsuccessful. As a possible alternative, the Rare-Earth system 163Ho - 163Dy is briefly discussed.
