Minimal archi-texture for neutrino mass matrices

The origin of the observed masses and mixing angles of quarks and leptons is one of imperative subjects in and beyond the standard model. Toward a deeper understanding of flavor structure, we investigate in this paper the minimality of fermion mass (Yukawa) matrices in unified theory. That is, the simplest matrix form is explored in light of the current experimental data for quarks and leptons, including the recent measurements of quark CP violation and neutrino oscillations. Two types of neutrino mass schemes are particularly analyzed; (i) Majorana masses of left-handed neutrinos with unspecified mechanism and (ii) Dirac and Majorana masses introducing three right-handed neutrinos. As a result, new classes of neutrino mass matrices are found to be consistent to the low-energy experimental data and high-energy unification hypothesis. For distinctive phenomenological implications of the minimal fermion mass textures, we discuss flavor-violating decay of charged leptons, the baryon asymmetry of the universe via thermal leptogenesis, neutrino-less double beta decay, and low-energy leptonic CP violation.Comment: 37 pages, 6 figure

On Neutrinos and Fermionic Mass Patterns

Recent data on neutrino mass differences are consistent with a hierarchical neutrino mass structure strikingly similar to what is observed for the other fermionic masses.Comment: 8pages, 2figure

Relation between CKM and MNS Matrices Induced by Bi-Maximal Rotations in the Seesaw Mechanism

It is found that the seesaw mechanism not only explains the smallness of neutrino masses but also accounts for the large mixing angles simultaneously, even if the unification of the neutrino Dirac mass matrix with that of up-type quark sector is realized. In this mechanism, we show that the mixing matrix of the Dirac-type mass matrix gets extra rotations from the diagonalization of Majorana mass matrix. Assuming that the mixing angles to diagonalize the Majorana mass matrix are extremely small, we find that the large mixing angles of leptonic sector found in atmospheric and long baseline reactor neutrino oscillation experiments can be explained by these extra rotations. We also find that provided the mixing angle around y-axis to diagonalize the Majorana mass matrix vanishes, we can derive the information about the absolute values of neutrino masses and Majorana mass responsible for the neutrinoless double beta decay experiment through the data set of neutrino experiments. In the simplified case that there is no CP phase, we find that the neutrino masses are decided as $m_1:m_2:m_3\approx 1:2:8$ and that there are no solution which satisfy $m_3<m_1<m_2$ (inverted mass spectrum). Then, including all CP phases, we reanalyze the absolute values of neutrino masses and Majorana mass responsible for the neutrinoless double beta decay experiment.Comment: 19 pages, 7 figures, revtex4, to appear in J.PHYS.SOC.JA

Search for Neutrinos from Annihilation of Captured Low-Mass Dark Matter Particles in the Sun by Super-Kamiokande

Artículo escrito por muchos autores, sólo se referencian el primero, los autores que firman como Universidad Autónoma de Madrid y el grupo de colaboración en el caso de que aparezca en el artículoSuper-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c2-200-GeV/c2) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV/c2 (at 10 GeV/c2, 1.49×10-39 cm2 for χχ→bb¯ and 1.31×10-40 cm2 for χχ→τ+τ- annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c2 mass rangeThe Super-Kamiokande experiment was built and has been operated with funding from the Japanese Ministry of Education, Culture, Sports, Science and Technology, the U.S. Department of Energy, and the U.S. National Science Foundatio