Browsing by Author "Shindou, Tetsuo"

Now showing 1 - 6 of 6
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    Charged Lepton Decays L_i to L_j + gamma, Leptogenesis CP-Violating Parameters and Majorana Phases
    (2006-06-13T07:46:15Z) Petcov, Serguey T.; Shindou, Tetsuo; Physics; Elementary Particle Theory
    We analyse the dependence of the rates of the LFV charged lepton decays mu to e + gamma, tau to e + gamma, tau to mu + gamma (l_i to l_j + gamma) and their ratios, predicted in the class of SUSY theories with see-saw mechanism of nu-mass generation and soft SUSY breaking with universal boundary conditions at the GUT scale, on the Majorana CP-violation phases in the PMNS neutrino mixing matrix and the ``leptogenesis'' CP-violating (CPV) parameters. The case of quasi-degenerate in mass heavy Majorana neutrinos is considered. The analysis is performed for normal hierarchical (NH), inverted hierarchical (IH) and quasi-degenerate (QD) light neutrino mass spectra. We show, in particular, that for NH and IH nu-mass spectrum and negligible lightest neutrino mass, all three l_i to l_j + gamma decay branching ratios, BR(l_i to l_j + gamma), depend on one Majorana phase, one leptogenesis CPV parameter and on the 3-neutrino oscillation parameters; if the CHOOZ mixing angle theta_13 is sufficiently large, they depend on the Dirac CPV phase in the PMNS matrix. The ``double ratios'' R(21/31) sim BR(mu to e + gamma)/BR(tau to e + gamma) and R(21/32) sim BR(mu to e + gamma)/BR(tau to mu + gamma) are determined by these parameters. The same Majorana phase enters into the NH and IH expressions for the effective Majorana mass in neutrinoless double beta decay, .
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    CP violation due to multi Froggatt-Nielsen fields
    (2007-05-15T12:00:46Z) Kanemura, Shinya; Matsuda, Koichi; Ota, Toshihiko; Petcov, Serguey T.; Shindou, Tetsuo; Takasugi, Eiichi; Physics; Elementary Particle Theory
    We study how to incorporate CP violation in the Froggatt--Nielsen (FN) mechanism. To this end, we introduce non-renormalizable interactions with a flavor democratic structure to the fermion mass generation sector. It is found that at least two iso-singlet scalar fields with imposed a discrete symmetry are necessary to generate CP violation due to the appearance of the relative phase between their vacuum expectation values.
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    Enhancement of lepton flavor violation in a model with bi-maximal mixing at the grand unification scale
    (2005) Kanemura, Shinya; Matsuda, Koichi; Ota, Toshihiko; Shindou, Tetsuo; Takasugi, Eiichi; Tsumura, Koji; Physics; Elementary Particle Theory
    We study phenomenological predictions in the scenario with the quasi-degenerate relation among neutrino Dirac masses, m_D1 simeq m_D2 < m_D3, assuming the bi-maximal mixing at the grand unification scale in supersymmetric standard models with right-handed neutrinos. A sufficient lepton number asymmetry can be produced for successful leptogenesis. The lepton flavor violating process mu to e gamma can be enhanced due to the Majorana phase, so that it can be detectable at forthcoming experiments. The processes tau to e gamma and tau to mu gamma are suppressed because of the structure of neutrino Dirac masses, and their branching ratios are smaller than that of mu to e gamma.
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    Majorana CP-Violating Phases, RG Running of Neutrino Mixing Parameters and Charged Lepton Flavour Violating Decays
    (2005) Petcov, Serguey T.; Shindou, Tetsuo; Takanishi, Yasutaka; Physics; Elementary Particle Theory
    We consider the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with flavour-universal boundary conditions at the GUT scale, in which the lepton flavour violating (LFV) decays µ → epsilon + gamma, tau → µ + gamma, etc., are predicted with rates that can be within the reach of present and planned experiments. These predictions depend critically on the matrix of neutrino Yukawa couplings Yv which can be expressed in terms of the light and heavy right-handed (RH) neutrino masses, neutrino mixing matrix UPMNS, and an orthogonal matrix R. We investigate the effects of Majorana CP-violation phases in UPMNS, and of the RG running of light neutrino masses and mixing angles from MZ to the RH Majorana neutrino mass scale MR, on the predictions for the rates of LFV decays µ → epsilon + gamma, tau → µ+gamma and tau → epsilon+gamma. Results for neutrino mass spectrum with normal hierarchy, values of the lightest v-mass in the range 0 ≤ m1 ≤ 0.30 eV, and quasi-degenerate heavy RH Majorana neutrinos in the cases of R = 1 and complex matrix R are presented. We find that the effects of the Majorana CP-violation phases and of the RG evolution of neutrino mixing parameters can change by few orders of magnitude the predicted rates of the LFV decays µ → epsilon+gamma and tau → epsilon + gamma. The impact of these effects on the tau→µ+gamma decay rate is typically smaller and only possible for m1 >∼ 0.10 eV. If the RG running effects are negligible, in a large region of soft SUSY breaking parameter space the ratio of the branching ratios of the µ → epsilon + gamma and tau → epsilon + gamma (tau → µ + gamma) decays is entirely determined in the case of R ~= 1 by the values of the neutrino mixing parameters at MZ.
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    Phase effects from the general neutrino Yukawa matrix on lepton flavor violation
    (2005) Kanemura, Shinya; Matsuda, Koichi; Ota, Toshihiko; Shindou, Tetsuo; Takasugi, Eiichi; Tsumura, Koji; Physics; Elementary Particle Theory
    We examine contributions from Majorana phases to lepton flavor violating processes in the framework of the minimal supersymmetric standard model with heavy right-handed neutrinos. All phases in the complex neutrino Yukawa matrix are taken into account in our study.
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    The See-Saw Mechanism, Neutrino Yukawa Couplings, LFV Decays l_i to l_j + gamma and Leptogenesis
    (2005) Petcov, Serguey T.; Rodejohann, Werner; Shindou, Tetsuo; Takanishi, Yasutaka; Physics; Elementary Particle Theory
    The LFV charged lepton decays mu to e + gamma, tau to e + gamma and tau to mu + gamma and thermal leptogenesis are analysed in the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with universal boundary conditions. The case of hierarchical heavy Majorana neutrino mass spectrum, M_1 << M_2 << M_3, is investigated.