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Hiroshi Okada

Publications and source records attributed to Hiroshi Okada.

At least 217 records · Page 12Linked to original sources
arXiv2013

Phenomenology of S_4 Flavor Symmetric extra U(1) model

We study several phenomenologies of an E_6 inspired extra U(1) model with S_4 flavor symmetry. With the assignment of left-handed quarks and leptons to S_4-doublet, SUSY flavor problem is softened. As the extra Higgs bosons are neutrinophilic, baryon number asymmetry in the universe is realized by leptogenesis without causing gravitino overproduction. We find that the allowed region for the lightest chargino mass is given by 100-140 GeV, if the dark matter is a singlino dominated neutralino whose mass is about 36 GeV.

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arXiv2013

Two Loop Radiative Seesaw Model with Inert Triplet Scalar Field

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 Higgs boson. We also discuss phenomenology of the inert triplet scalar bosons, especially focusing on the doubly-charged scalar bosons at Large Hadron Collider in parameter regions constrained by the electroweak precision data and WMAP data. We study how we can distinguish our model from the minimal Higgs triplet model.

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arXiv2013

Light Dark Matter Candidate in B-L Gauged Radiative Inverse Seesaw

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 by the experiments such as CoGeNT and XENON (2012).

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arXiv2012

Dark Matters in Gauged B-3L_i Model

We study a dark matter model with local B-3L_i symmetry that is known as anomaly free and requires a single right-handed neutrino. Here we have two dark matter candidates; that is, fermionic or bosonic one. We focus on analyzing each of the case within the light mass region, which is required by the perturbative theory of the Higgs quartic coupling.

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arXiv2012

Suppressing Proton Decay by Cancellation in S_4 Flavor Symmetric Extra U(1) Model

We consider proton stability based on E_6 inspired extra U(1) model with S_4 flavor symmetry. In this model, a long life time of proton is realized by the flavor symmetry. One of the interesting effects of flavor symmetry is that the proton decay widths of p -> mu^+, X are suppressed by cancellation. This suppression mechanism is important in the case that Yukawa coupling constants are hierarchical. Our model predicts p -> e^+, K^0 has larger decay width than that of p -> mu^+, K^0.

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arXiv2012

Higgs Signatures in Inverse Seesaw Model at the LHC

In the inverse seesaw mechanism where the spontaneously broken B-L symmetry induces tiny B-L violating Majorana masses for right-handed neutrinos, non-standard Higgs signatures can arise due to a possible Higgs doublet and singlet mixing and/or Higgs boson decays to a left- and right-handed neutrino. This leads to a remarkable feature of hadronically quiet di-lepton final states which can exhibit, in particular, lepton flavour violating signatures coming from flavour-dependent neutrino Yukawa couplings. In this process, one lepton coming from the right-handed decay could be soft enough can be missed by the trigger level cuts of CMS and ATLAS for the di-lepton plus missing energy signature. The prospects of such a signature are investigated for 8 TeV and 14 TeV center of mass energy of the LHC, taking the maximum value of the allowed neutrino Yukawa coupling and the right-handed neutrino mass of 100 GeV. A PYTHIA level simulation shows that the integrated luminosity of 10--20/fb and 1.6/fb for 8 TeV is required to observe the inclusive leptonic and lepton flavour violating signatures, respectively. For 14 TeV, the reach is more and a larger parameter space of the inverse seesaw model can be probed.

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arXiv2012

Fermionic Dark Matter in Radiative Inverse Seesaw Model with U(1)_{B-L}

We construct a radiative inverse seesaw model with local B-L symmetry, and investigate the flavor structure of the lepton sector and the fermionic Dark Matter. Neutrino masses are radiatively generated through a kind of inverse seesaw framework. The PMNS matrix is derived from each mixing matrix of the neutrino and charged lepton sector with large Dirac CP phase. We show that the annihilation processes via the interactions with Higgses which are independent on the lepton flavor violation, have to be dominant in order to satisfy the observed relic abundance by WMAP. The new interactions with Higgses allow us to be consistent with the direct detection result reported by XENON100, and it is possible to verify the model by the exposure of XENON100 (2012).

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arXiv2012

Can A Higgs Portal Dark Matter be Compatible with the Anti-proton Cosmic-ray?

Recent direct detection experiments of Dark Matter (DM), CoGeNT and DAMA implicate a light DM of a few GeV. Such a light DM would generate a large amount of anti-proton since suppression for anti-proton flux from DM annihilation is ineffective. We discuss whether a light dark matter with mass of 5-15 GeV, which is especially in favor of the recent experiments reported by CoGeNT, is compatible with the anti-proton no excess in the cosmic-ray. In view of the direct detection of DM and no anti-proton excess in the cosmic-ray both, we show that a Dirac DM is favored than a scalar one since there is no s-wave of the annihilation cross section for the Dirac DM. A large elastic cross section for direct detection can be obtained through the additional light Higgs exchange. We show an allowed region that simultaneously satisfies the DM relic density, the elastic cross section favored by CoGeNT and also the constraint of H_L Z Z coupling of the light Higgs boson by LEP.

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arXiv2012

Non-zero θ_{13} linking to Dark Matter from Non-Abelian Discrete Flavor Model in Radiative Seesaw

We propose a new scenario in a radiative seesaw model based on A_4 flavor symmetry. In this model, we explore a possibility of linking non-zero θ_{13} to dark matter. And we analyze the lepton sector to predict the observed neutrinos and mixings, especially obtaining a lower bound of θ_{13}~3.5 [Deg.]. We show that the non-zero θ_{13} is correlated with our heavy Majorana type of dark matter. Also we predict that the mass be O(1-10) TeV, as a result of analyzing the Wilkinson-Microwave-Anisotropy-Probe and lepton flavor violation.

hep-ph↗
arXiv2012

Proton Stability in S_4 x Z_2 Flavor Symmetric Extra U(1) Model

We consider proton stability based on E_6 inspired extra U(1) model with S_4 x Z_2 flavor symmetry. In this model, a long life time of proton is realized by the flavor symmetry in several ways. We classify the suppression mechanisms of proton-decay and explain how the flavor symmetry works. There is an interesting solution, such as, in a special direction of vacuum expectation value (VEV), baryon number violating interactions are canceled. In the case that the suppression of proton decay is realized by the appropriate size of VEV, the allowed region of VEV exists when the exotic quark mass is O(TeV). From the constraint for the life time of exotic quark, the right handed neutrino mass should be in narrow range around 10^{12} GeV.

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arXiv2011

Lepton Flavor Model and Decaying Dark Matter in The Binary Icosahedral Group Symmetry

We propose a new flavor model that can simlutaneously well-describe the indirect detection experiment of (decaying) dark matter in the cosmic-ray, with the binary icosahedral group A'_5. We show not only that the A'_{5} symmetry can derive quark and lepton masses and mixings consistently, but also that are expected some predictions for the lepton sector. And if we assume a gauge-singlet fermionic decaying dark matter, its decay operators are also constrained by this symmetry so that only dimension six operators of leptonic decay are allowed up to six dimensional Lagrangians. We find that the cosmic-ray anomalies reported by PAMELA and Fermi-LAT are well explained by decaying dark matter controlled by the A'_{5} flavor symmetry, which induces universal decays.

hep-ph↗
arXiv2011

Two Component Dark Matters in S_4 x Z_2 Flavor Symmetric Extra U(1) Model

We study cosmic-ray anomaly observed by PAMELA based on E_6 inspired extra U(1) model with S_4 x Z_2 flavor symmetry. In our model, the lightest flavon has very long lifetime of O(10^{18)) second which is longer than the age of the universe, but not long enough to explain the PAMELA result ~ O(10^{26}) sec. Such a situation could be avoidable by considering that the flavon is not the dominant component of dark matters and the dominant one is the lightest neutralino. With appropriate parameter set, density parameter of dark matter and over-abundance of positron flux in cosmic-ray are realized at the same time. There is interesting correlation between spectrum of positron flux and V_{MNS}. No excess of anti-proton in cosmic-ray suggests that sfermions are heavier than 4 TeV and the masses of the light Higgs bosons are degenerated.

hep-ph↗
arXiv2011

A light Scalar Dark Matter for CoGeNT and DAMA in D_6 Flavor Symmetric Model

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 elastic cross section σ\simeq 7x10^{-41} cm^2 which is required by these experiments. Our dark matter interacts with a D_6 singlet scalar Higgs boson, which couples only to quark sector. The dark matter-nucleon cross section and new decay mode h->DM DM can be large if the standard model Higgs boson h is light. The Higgs phenomenology is also discussed.

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arXiv2011

Right-handed Sneutrino Dark Matter in Supersymmetric B-L Model

We show that the lightest right-handed sneutrino in TeV scale supersymmetric B-L model with inverse seesaw mechanism is a viable candidate for cold dark matter. We find that it accounts for the observed dark matter relic abundance in a wide range of parameter space. The spin-independent cross section of B-L right-handed sneutrino is consistent with the recent results CDMS II and XENON experiments and it is detectable in future direct detection experiments. Although the B-L right-handed sneutrinos annihilate into leptons, the PAMELA results can not be explained in this model unless a huge boost factor is considered. Also the muon flux generated by B-L right-handed sneutrino in the galactic center is smaller than Super-Kamiokande's upper bound.

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arXiv2011

Direct and Indirect Detection of Dark Matter in D6 Flavor Symmetric Model

We study a fermionic dark matter in a non-supersymmetric extension of the standard model with a family symmetry based on D6xZ2xZ2. 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 of 230 GeV - 750 GeV in the WMAP analysis combined with mu to e gamma constraint. Moreover we simultaneously explain the experiments of direct and indirect detection, by simply adding a gauge and D6 singlet real scalar field. In the direct detection experiments, we show that the lighter dark matter mass ~ 230 GeV and the lighter standard model Higgs boson ~ 115 GeV is in favor of the observed bounds reported by CDMS II and XENON100. In the indirect detection experiments, we explain the positron excess reported by PAMELA through the Breit-Wigner enhancement mechanism. We also show that our model is consistent with no antiproton excess suggested by PAMELA.

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arXiv2011

T(13) Flavor Symmetry and Decaying Dark Matter

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 fermionic decaying dark matter, its decay operators are also constrained by the T_{13} symmetry so that only dimension six operators of leptonic decay are allowed. We find that the cosmic-ray anomalies reported by PAMELA and Fermi-LAT are explained by decaying dark matter controlled by the T_{13} flavor symmetry.

hep-ph↗
arXiv2011

Observable T_7 Lepton Flavor Symmetry at the Large Hadron Collider

More often than not, models of flavor symmetry rely on the use of nonrenormalizable operators (in the guise of flavons) to accomplish the phenomenologically successful tribimaximal mixing of neutrinos. We show instead how a simple renormalizable two-parameter neutrino mass model of tribimaximal mixing can be constructed with the non-Abelian discrete symmetry T_7 and the gauging of B-L. This is also achieved without the addition of auxiliary symmetries and particles present in almost all other proposals. Most importantly, it is verifiable at the Large Hadron Collider.

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