Yuji Kajiyama

National Institute of Chemical Physics and Biophysics | KBFI · Laboratory of High Energy and Computational Physics

We discuss two Higgs doublet models with a softly-broken discrete S3S3 symmetry, where the mass matrix for charged-leptons is predicted as the diagonal form in the weak eigenbasis of lepton fields. Similarly to an introduction of Z2Z2 symmetry, the tree level flavor changing neutral current can be forbidden by imposing the S3S3 symmetry to the mode...

We investigate the Majorana neutrino mass matrix $M_{\nu}$ with one parameter in the context of two texture zeros and its symmetry realization by non-Abelian discrete symmetry. From numerical calculation, we confirm that the textures $(M_{\nu})_{11,12}=0$ and $(M_{\nu})_{11,13}=0$ are consistent with the current experimental constraints, and show t...

We propose a hybrid seesaw model based on the $S_3$ flavor symmetry. The mass matrix for neutrino is generated via the type-II seesaw mechanism at tree level in combination with one-loop level. On the other hand, the mass matrix for charged lepton is predicted as a diagonal form without introducing any unitary matrices. In this model, there are two...

We propose a new type of radiative seesaw model in which observed neutrino masses are generated through a three-loop level diagram in combination with tree-level type-II seesaw mechanism in a renormalizable theory. We introduce a Non-abelian flavor symmetry $T_7$ in order to constrain the form of Yukawa interactions and Higgs potential. Although se...

The recent result of the AMS-02 experiment shows small deviation from the fitting curve at around 125 GeV of the positron energy. In this paper, we propose a new interpretation of the data that it originates from decay of two (heavier and lighter) Dark Matter (DM) components and corresponds to the threshold of the lighter DM component. When DM deca...

We construct a loop induced seesaw model in a TeV scale theory with gauged U(1)_{B-L} symmetry. Light neutrino masses are generated at two-loop level and right-handed neutrinos also obtain their masses by one-loop effect. Multi-component Dark Matters (DMs) are included in our model due to the remnant discrete symmetry after the B-L symmetry breakin...

We propose a radiative seesaw model with an inert triplet scalar field in which Majorana neutrino masses are generated at the two loop level. There are fermionic or bosonic dark matter candidates in the model. We find that each candidate can satisfy the WMAP data when its mass is taken to be around the half of the mass of the standard model like Hi...

We study a radiative inverse seesaw model with local B-L symmetry, in which we extend the neutrino mass structure that is generated through a kind of inverse seesaw framework to the more generic one than our previous work. We focus on a real part of bosonic particle as a dark matter and investigate the features in O(1-80) GeV mass range, reported b...

It is appealing to stabilize dark matter by the same discrete symmetry that is used to explain the structure of quark and lepton mass matrices. However, to generate the observed fermion mixing patterns, any flavor symmetry must necessarily be broken, rendering dark matter unstable. We study singlet, doublet and triplet SU(2) multiplets of both scal...

We try to interpret a very light dark matter with mass of 5~10 GeV which is in favor of the recent experiments reported by CoGeNT and DAMA, in a non-supersymmetric extension of radiative seesaw model with a family symmetry D_6 x Z_2 x Z_2. We show that a D_6 singlet real scalar field can be a promising dark matter candidate, and it gives the elasti...

We study fermionic dark matter in a non-supersymmetric extension of the standard model with a family symmetry based on . In our model, the final state of the dark matter annihilation is determined to be e + e − by the flavor symmetry, which is consistent with the PAMELA result. At first, we show that our dark matter mass should be within the range...

The like-sign dimuon charge asymmetry of the B meson, which was reported in the DØ Collaboration, is studied in the SU(5) SUSY GUT model with S4 flavor symmetry. Additional CP violating effects from the squark sector are discussed in Bs-B̅s mixing process. The predicted like-sign charge asymmetry is in the 2σ range of the combined result of DØ and...

The positron anomaly recently reported by the cosmic-ray measurements can be explained by the decaying dark matter scenario, where it decays mainly into leptons with the lifetime of O(1026) s. When the dark matter is a fermionic particle, the lifetime of this order is known to be obtained by a dimension 6 operator suppressed by the unification scal...

We study a new flavor symmetric model with non-Abelian discrete symmetry T_{13}. The T_{13} group is isomorphic to Z_{13} \rtimes Z_3, and it is the minimal group having two complex triplets as the irreducible representations. We show that the T_{13} symmetry can derive lepton masses and mixings consistently. Moreover, if we assume a gauge-singlet...

We propose a new leptogenesis scenario in a gauged $B-L$ model with supersymmetry at the TeV energy scale. Instead of relying on the very small Yukawa couplings of the singlet neutrinos $N^c$ to generate the observed baryon asymmetry of the Universe, which requires a very large resonance enhancement, their $B-L$ gauge interactions are invoked. Succ...

We analyze the connection between electric dipole moment of the electron and the soft leptogenesis in supersymmetric B–L extension of the Standard Model. In this model, the B–L symmetry is radiatively broken at TeV scale. Therefore, it is a natural framework for low scale seesaw mechanism and also for implementing the soft leptogenesis. We show tha...

We present and study a novel electroweak-scale leptogenesis mechanism occurring in U(1)_F flavor symmetric two Higgs doublet models with Higgs-dependent Yukawa couplings. In this scenario CP-violation originates entirely from the Higgs sector, and large CP asymmetries in TeV scale heavy neutrino decays can be obtained without resonance enhancement...

This chapter of the report of the ``Flavor in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure o...

We study the effects of unparticle physics on muon g - 2 and lepton flavor violating (LFV) tau decay processes. LFV interactions between the standard model sector and unparticles can explain the difference of the experimental value of muon g - 2 from the standard model prediction. While the same couplings generate LFV tau decay, we found that LFV c...

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structu...

In this talk, we investigate Lepton Flavor Violating (LFV) tau decay by R-Parity Violating (RPV) operators controlled by a non-Abelian discrete $Q_6$ family symmetry. We assume that only a family symmetry determines the whole flavor structure of a model, and the model indicates specific predictions of LFV tau decay processes by RPV operators. We pr...

We present a simple texture that predicts the cotangent of the solar neutrino mixing angle to be equal to the golden ratio. This prediction is 1.4 standard deviations below the present best-fit value and final SNO and KamLAND data could discriminate it from tri-bi-maximal mixing. The neutrino mass matrix is invariant under a Z_2 x Z'_2 symmetry: th...

We investigate the implications of R-parity violating operators in a model with family symmetry. The family symmetry can determine the form of R-parity violating operators as well as the Yukawa matrices responsible for fermion masses and mixings. In this paper we consider a concrete model with non-abelian discrete symmetry Q_6 which contains only t...

We consider a nonsupersymmetric extension of the standard model with a family symmetry based on DxZxZ, where one of Z's is exactly conserved. This Z forbids the tree-level neutrino masses and simultaneously ensures the stability of cold dark matter candidates. From the assumption that cold dark matter is fermionic we can single out the D singlet ri...

We consider a supersymmetric extension of the standard model, which possess a family symmetry based on a binary dihedral group Q 6, and investigate the consequences of the family symmetry on the mixing of fermions, FCNCs and the stability of proton.

We consider a non-supersymmetric extension of the standard model with a family symmetry based on D6 Z2 Z2, where one of Z2's is exactly conserved. This Z2 forbids the tree-level neutrino masses and simultaneously ensures the stability of cold dark matter candidates. From the assumption that cold dark matter is fermionic we can single out the D6 sin...

Family symmetry could explain large mixing of the atmospheric neutrinos. The same symmetry could explain why the flavor changing current processes in supersymmetric standard models can be so suppressed. It also may be able to explain why the proton is so stable. We investigate these questions in a supersymmetric, renormalizable extension of the sta...

A concrete model which can suppress FCNCs and CP violating phenomena is suggested. It is an $S_3$ symmetric extension of the MSSM in extra dimensions, where only SU(2) and SU(3) gauge multiplets are assumed to propagate in the bulk. They are suppressed due to $S_3$ flavor symmetry at $M_{SUSY}$, and the infrared attractive force of gauge interactio...

The infrared attractive force of the bulk gauge interactions is applied to soften the supersymmetric flavor problem in the orbifold SU(5) grand unified theory of Kawamura. Then this force aligns in the infrared regime the soft supersymmetry breaking terms out of their anarchical disorder at a fundamental scale, in such a way that flavor-changing ne...

A mechanism for double suppression of flavor-changing neutral currents (FCNCs) and CP violating phases in supersymmetric models is suggested. At M_{SUSY} they are suppressed due to a nonabelian discrete flavor symmetry, and the infrared attractive force of gauge interactions in extra dimensions are used to suppress them at the compactification scal...