Neutrinoless Double Beta Decay Constraints

A brief overview is given of theoretical analyses with neutrinoless double beta decay experiments. Theoretical bounds on the ``observable'', _betabeta, are presented. By using experimental bounds on _betabeta, allowed regions are obtained on the m_l-cos{2theta_12} plane, where m_l stands for the lightest neutrino mass. It is shown that Majorana neutrinos can be excluded by combining possible results of future neutrinoless double beta decay and {}^3H beta decay experiments. A possibility to constrain one of two Majorana phases is discussed also.Comment: 8 pages, 6 figures, ws-procs9x6.cls. Invited talk at 4th Workshop on Neutrino Oscillations and their Origin (NOON2003), Kanazawa, Japan, 10-14 Feb 200

Exploring Leptonic CP Violation with Combined Analysis of Reactor and Neutrino Superbeam Experiments

We investigate the possibility to find the leptonic CP-violation by combining the reactor experiment with the superbeam experiment without antineutrino superbeam. We show also how much the sensitivity on CP-violating phase delta is affected by the fact that we have not known the sign of Delta m^2_31.Comment: 4 pages, 5 eps-files, ws-procs10x7.cls, talk at the 32nd International Conference on High Energy Physics (ICHEP04), Aug. 16-22, 2004, Beijing, Chin

Constraints on Neutrino Parameters by Neutrinoless Double Beta Decay Experiments

Allowed regions on the m_l - cos{2\theta_{12}} plane are extracted from results of neutrinoless double beta decay experiments. It is shown that 0.05 eV (0 eV) < m_l < 1.85 eV is obtained for the normal (inverted) hierarchy by using the LMA best fit parameters and the 0\nu\beta\beta result announced late last year, which is 0.05 eV _\beta\beta < 0.84 eV with +/- 50% uncertainty of the nuclear matrix elements.Comment: 6 pages, 3 figures, iopart.cls. Invited talk at Beyond the Desert02, Oulu, Finland, 2-7 June 200

Probing Models of Neutrino Masses via the Flavor Structure of the Mass Matrix

We discuss what kinds of combinations of Yukawa interactions can generate the Majorana neutrino mass matrix. We concentrate on the flavor structure of the neutrino mass matrix because it does not depend on details of the models except for Yukawa interactions while determination of the overall scale of the mass matrix requires to specify also the scalar potential and masses of new particles. Thus, models to generate Majorana neutrino mass matrix can be efficiently classified according to the combination of Yukawa interactions. We first investigate the case where Yukawa interactions with only leptons are utilized. Next, we consider the case with Yukawa interactions between leptons and gauge singlet fermions, which have the odd parity under the unbroken Z_2 symmetry. We show that combinations of Yukawa interactions for these cases can be classified into only three groups. Our classification would be useful for the efficient discrimination of models via experimental tests for not each model but just three groups of models.Comment: 14 pages, 9 eps files, references adde

Exploring Leptonic CP Violation by Reactor and Neutrino Superbeam Experiments

We point out the possibility that reactor measurement of theta_{13}, when combined with high-statistics nu_e appearance accelerator experiments, can detect leptonic CP violation. Our proposal is based on a careful statistical analysis under reasonable assumptions on systematic errors, assuming 2 years running of the neutrino mode J-PARC -> Hyper-Kamiokande experiment and a few years running of a reactor experiment with 100 ton detectors at the Kashiwazaki-Kariwa nuclear power plant. We show that the method can be arranged to be insensitive to the intrinsic parameter degeneracy but is affected by the one due to unknown sign of Delta m^2_{31}.Comment: 18 pages, 5 figures, uses revtex4 and graphicx, revised treatment of parameter degeneracy due to unknown sign of Dm^2 and tightened CP sensitivity by using projected chi^