Junji Hisano

Bulk Standard Model in the Randall-Sundrum Background

We discuss issues in an attempt to put the standard model (SM) in five-dimensional anti\char21{}de Sitter spacetime compactified on

New parametrization of the seesaw mechanism and applications in supersymmetric models

{S}^{1}{/Z}_{2}.

Neutrino masses, muon g − 2, and lepton-flavour violation in the supersymmetric see-saw model

The recently proposed approach to the gauge hierarchy problem by using this background geometry, with the SM confined on a boundary, is extended to a situation where (some of) the SM particles reside in the five-dimensional bulk. In particular, we find a localization of zero modes of bulk fermions near the boundary with a negative tension. Unlike the compactification with the flat metric, these fermion zero modes couple to Kaluza-Klein (KK) excitations of the SM gauge bosons. Interestingly, only low-lying modes of such KK gauge bosons have non-negligible couplings. Current electroweak precision data give a constraint that the first KK mode be heavier than

CP Violation in the Minimal Supersymmetric Seesaw Model

9

Atmospheric neutrino oscillation and large lepton-flavour violation in the SUSY SU(5) GUT

TeV. We also argue that at least the Higgs field should be confined on the brane to utilize the Randall-Sundrum background as a solution to the gauge hierarchy.

Lepton electric dipole moments in non-degenerate supersymmetric seesaw models

We present a new parametrization of the minimal seesaw model, expressing the heavy-singlet neutrino Dirac Yukawa couplings (Y n) ij and Majorana masses MNi in terms of effective light-neutrino observables and an auxiliary Hermitian matrix H. In the minimal supersymmetric version of the seesaw model, the latter can be related directly to other low-energy observables, including processes that violate charged lepton flavor and CP . This parametrization enables one to respect the stringent constraints on muon-number violation while studying the possible ranges for other observables by scanning over the allowed parameter space of the model. Conversely, if any of the lepton-flavor-violating process is observed, this measurement can be used directly to constrain ( Y n) ij and MN i . As applications, we study flavor-violating t decays and the electric dipole moments of leptons in the minimal supersymmetric seesaw model.

Lepton flavor violation in the left-handed slepton production at future lepton colliders

In the light of the recent muon (g 2) result by the E821 experiment at the Brookhaven National Laboratory, we study the event rates of the charged leptonflavour-violating (LFV) processes in the supersymmetric standard model (SUSY SM) with the heavy right-handed neutrinos (SUSY see-saw model). Since the left-handed sleptons get the LFV masses via the neutrino Yukawa interaction in this model, the event rate of ! e and the SUSY-SM correction to (g 2)=2 (a SUSY ) are strongly correlated. When the left-handed sleptons have a LFV mass between the rst and second generations ((m 2 ~ L )12) in the mass matrix, it should be suppressed by 10 3 (10 9 =a SUSY ) compared with the diagonal components (m 2 ), from the current experimental bound on ! e. The recent (g 2) result indicates a SUSY 10 9 . The future charged LFV experiments could cover (m 2 ~ L )12=m 2 > 10 (5 6) . These experiments will give a signicant impact on the flavour models and the SUSY-breaking models. In the typical models where the neutrino oscillation results are explained and the top quark and tau neutrino Yukawa couplings are unied at the GUT scale, a large LFV mass of (m 2 ~ L )12=m 2 > 10 4 is generated, and the large LFV event rates are predicted. We impose a so-called no-scale condition for the SUSY-breaking parameters at the GUT scale, which suppress the FCNC processes, and derive the conservative lower bound on ! e. The predicted Br( ! e) could be covered at the future LFV experiments.

Natural effective supersymmetry

Abstract We study CP violation in the lepton sector of the supersymmetric extension of the Standard Model with three generations of massive singlet neutrinos with Yukawa couplings Yν to lepton doublets, in a minimal seesaw model for light neutrino masses and mixing. This model contains six physical CP-violating parameters, namely the phase δ observable in oscillations between light neutrino species, two Majorana phases φ1,2 that affect ββ0ν decays, and three independent phases appearing in Y ν Y ν † , that control the rate of leptogenesis. Renormalization of the soft supersymmetry-breaking parameters induces observable CP violation at low energies, including T-odd asymmetries in polarized μ→eee and τ→lll decays, as well as lepton electric dipole moments. In the leading-logarithmic approximation in which the massive singlet neutrinos are treated as degenerate, these low-energy observables are sensitive via Y ν † Y ν to just one combination of the leptogenesis and light-neutrino phases. We present numerical results for the T-odd asymmetry in polarized μ→eee decay, which may be accessible to experiment, but the lepton electric dipole moments are very small in this approximation. To the extent that the massive singlet neutrinos are not degenerate, low-energy observables become sensitive also to two other combinations of leptogenesis and light-neutrino phases, in this minimal supersymmetric seesaw model.

Exact event rates of lepton flavor violating processes in supersymmetric SU(5) model [Phys. Lett. B 391 (1997) 341]

Abstract The atmospheric neutrino anomaly reported by the super-Kamiokande collaboration suggests existence of a large flavour violating Yukawa coupling. We discuss lepton-flavour violation at low energies in the supersymmetric (SUSY) SU(5)GUT model with right-handed neutrinos assuming the hidden-sector SUSY breaking scenario in the minimal supergravity. We find that for a wide range of parameter space suggested from the atmospheric neutrino anomaly, if the tau-neutrino Yukawa coupling is as large as that of top quark, lower bounds of the branching ratios of μ+→e+γ, τ±→μ±γ, and the μ−e conversion rate on 22 48 Ti become around 10−14, 10−9, and 10−16, respectively. These reaction rates may be in the region accessible by near future experiments.

Enhancement of mu ---> e gamma in the supersymmetric SU(5) GUT at large tan Beta

Abstract In the context of supersymmetric seesaw models of neutrino masses with non-degenerate heavy neutrinos, we show that Dirac Yukawa interactions Nci(Yν)ijLjH2 induce large threshold corrections to the slepton soft masses via renormalization. While still yielding rates for lepton-flavour-violating processes below the experimental bounds, these contributions may increase the muon and electron electric dipole moments dμ and de by several orders of magnitude. In the leading logarithmic approximation, this is due to three additional physical phases in Yν, one of which also contributes to leptogenesis. The naive relation dμ/de≈−mμ/me is violated strongly in the case of successful phenomenological textures for Yν, and the values of dμ and/or de may be within the range of interest for the future experiments.