Tsuneyuki Kotani

CP violation in Majorana neutrinos

We discuss CP violation in a massive Majorana neutrino system. In general, for the n-Majorana neutrino system (n = number of generations) the number of CP-violation phases in n(n−1)/2 in contrast to the Dirac neutrino system where (n−1)(n−2)/2 phases are present. Therefore, the CP-violation effect appears even in the case of two generations. For neutrino oscillations, however, this number reduces to (n−1)(n−2)/2 due to the special combination of the unitary transformation matrix among the current neutrinos (ν) and mass neutrinos (N).

DOUBLE BETA DECAY

The double β decay is investigated by the use of the relativistic Coulomb wave function including the finite nuclear size effect. A general form of the V±A interactions is considered. It is shown that the decay rate is enhanced considerably in comparison with the case of the plane wave multiplied by the non-relativistic Fermi factor.

Pseudo Dirac Neutrino

There is a growing interest in the neutrino masses. Theoretically, there is much freedom in neutrino mass patterns in contrast to quarks and charged leptons because neutrinos are in general considered Majorana particles. Experimentally, the v-oscillation!) and the /3/3 decay2),3) give serious constraints to neutrino masses and their mixing scheme. A special case where there are degeneracies of Majorana neutrino masses has recently been interesting. If the degeneracy happens as a consequence of the special symmetry in the mass matrix, a pair of degenerate Majorana neutrinos may form a Dirac neutrino. This Dirac neutrino is called the pseudo Dirac (PD) neutrino,4)-6) if the symmetry of the mass matrix is not the symmetry of the weak interaction. That is, the lepton number assigned to this Dirac neutrino is not conserved in the weak interaction and thus the mass degeneracy is removed by the higher order perturbation of the weak interaction. A PD neutrino has recently drawn special attention due to the tight neutrino mass bound obtained from the analysis of the /3/3 decay,2),3)

Neutrino Mass, the Right-Handed Interaction and the Double Beta Decay. II General Properties and Data Analysis

Based on the formulae for the double /3 decay obtained in the previous paper, the general properties of 0+ .... J+ transitions are discussed and the analysis of the experimental data is presented. It is found that, for the two neutrino mode, the 0+ .... 0+ transition in the two nucleon (2n)-mechanism dominates over the 0+ .... 2+ transition as well as the contribution from the N*mechanism. For the neutrino less mode, only the 0+ .... 0+ transition in the 2n-mechanism is allowed if there is no right-handed interaction. When the right-handed interaction gives a sizable contribution, the role of the 0+ .... 2+ transition becomes as important as the 0+ .... 0+ transition in this mode. It is concluded that the experimental data on the ratio of the 128Te to 130Te half-lives by Hennecke et al. suggest that neutrinos are Majorana particles, if we take the Vergados estimation of the nuclear matrix elements. Moreover, we find that the weighted average of neutrino masses is around 34 eV if there is no right-handed interaction.

Role of the nucleon recoil term in the neutrinoless double beta decay

Abstract Some potentials due to neutrino propagation in double beta decay appear as divergent integrals. We give a prescription to handle this divergence and then estimate the nucleon recoil term. We found that this contribution is of the same order as the electron P-wave effect. A new improved bound on the right-handed parameter η is derived.

Meson mass spectra in the quark-string model

Abstract Old and new meson spectra are studied from a unified view point based on the quark-string lagrangian which has been derived from a continuum limit of the lattice gauge theory. Calculated values for c c states agree with observed values within a few percent error. The ψ → η c γ process is discussed.

New parameterization in muon decay and the type of emitted neutrino

Normal muon decay, µ + → e + νeνµ, is studied as a tool to discriminate between the Dirac and Majorana types of neutrinos and to survey the structure of the weak interaction. It is assumed that massive neutrinos mix with one another and that the interaction Hamiltonian consists of the V − A and V + A charged currents. A new set of parameters used in place of the Michel parameters is proposed for the positron distribution. Explicit forms of these new parameters are obtained by assuming that the masses are less than 10 eV for light neutrinos and sufficiently large for heavy Majorana neutrinos, which are not emitted in the muon decay. It is shown that a possible method to discriminate between the Dirac and Majorana cases is to use a characterization given by the χ 2 fitting of their spectra. It is also confirmed that the theoretical predictions in the Majorana neutrino case are almost the same as those obtained from the standard model. Indeed, their differences cannot be distinguished within the present experimental precision.