arXiv subjects

Hiroshi Okada

Publications and source records attributed to Hiroshi Okada.

At least 127 records · Page 7Linked to original sources

arXiv2019

One-loop neutrino mass model with $SU(2)_L$ multiplet fields

We propose a one-loop neutrino mass model with several $SU(2)_L$ multiplet fermions and scalar fields in which the inert feature of a scalar to realize the one-loop neutrino mass can be achieved by the cancellation among Higgs couplings thanks to non-trivial terms in the Higgs potential and to present it in a simpler way. Then we discuss our typical cut-off scale by computing renormalization group equation for $SU(2)_L$ gauge coupling, lepton flavor violations, muon anomalous magnetic moment, possibility of dark matter candidate, neutrino mass matrix satisfying the neutrino oscillation data. Finally, we search for our allowed parameter region to satisfy all the constraints, and discuss a possibility of detecting new charged particles at the large hadron collider.

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arXiv2019

Inverse seesaw model with large $SU(2)_L$ multiplets and natural mass hierarchy

We propose an inverse seesaw model with large $SU(2)_L$ multiplet fields which realizes natural mass hierarchies among neutral fermions. Here, lighter neutral fermion mass matrices are induced via two suppression mechanisms; one is small vacuum expectation value of $SU(2)_L$ triplet required by rho parameter constraint and the other is generation of Majorana mass term of extra singlet fermions at one-loop level. To realize the loop masses, we impose $Z_2$ symmetry which also guarantees stability of a dark matter candidate. Furthermore, we discuss anomalous magnetic moment and collider physics from interactions of large multiplet fields.

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arXiv2019

A Linear seesaw model with hidden gauge symmetry

We propose a natural realization of linear seesaw model with hidden gauge symmetry in which $SU(2)_L$ triplet fermions, one extra Higgs singlet, doublet and quartet scalar are introduced. Small neutrino mass can be realized by two suppression factors that are small vacuum expectation value of quartet scalar and inverse of Dirac mass for triplet. After formulating neutrino mass matrix, we discuss collider phenomenology of the model focusing on signals from exotic charged particles production at the LHC.

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arXiv2019

Dark matter and $B$-meson anomalies in a flavor dependent gauge symmetry

A possibility of explaining the anomalies in the semileptonic $B$-meson decay $B \to K^{*} μ\barμ$ has been explored in the framework of the gauged $U(1)_{μ-τ}$ symmetry. Apart from the muon anomalous magnetic moment and neutrino sector, we formulate the model starting with a valid Lagrangian and consider the constraints from the neutral meson mixings, the bounds on direct detection and the relic density of the bosonic dark matter candidate augmented to collider constraints. We search the parameter space, which accommodates the size of the anomaly of the $B \rightarrow K^* μ\bar μ$ decay, to satisfy all experimental constraints. We found the allowed region on the plane of the dark matter and $Z'$ masses is a rather narrow compared to the previous analysis.

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arXiv2019

Radiative neutrino mass in an alternative $U(1)_{B-L}$ gauge symmetry

We propose a neutrino model in which neutrino masses are generated at one loop level and three right-handed fermions have non-trivial charges under $U(1)_{B-L}$ gauge symmetry in no conflict with anomaly cancellation. After the spontaneously symmetry breaking, a remnant $Z_2$ symmetry is induced and plays an role in assuring the stability of dark matter candidate.

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arXiv2019

An inverse seesaw model with natural hierarchy at TeV scale

We propose a new kind of inverse seesaw model without any additional symmetries. Instead of the symmetries, we introduce several fermions and bosons with higher $SU(2)_L$ representations. After formulating the Higgs sector and neutrino sector, we show that the cut-off energy, which is valid to our model, is at around TeV scale, by examining behavior of $SU(2)_L$ gauge coupling. Then we show the testability of our model at collider physics.

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arXiv2019

A Two Loop Radiative Neutrino Model

We explore the possibility to explain a bosonic dark matter candidate with a gauge singlet inside the loop to generate the neutrino mass matrix at two-loop level. The mass matrix is suppressed by a small mixing that comes from the bound on {direct detection experiments of the dark matter, and equivalent of the three-loop neutrino model due to the small mixing between neutral inert bosons. Here, our setup is} the Zee-Babu type scenario with $Z_3$ discrete symmetry, in which we consider the neutrino oscillation data, lepton flavor violations, muon $g-2$, $μ-e$ conversion rate, lepton flavor-changing and conserving $Z$ boson decay and bosonic dark matter candidate.

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arXiv2019

CP violation of quarks in $A_4$ modular invariance

We discuss the quark mass matrices in the $A_4$ modular symmetry, where the $A_4$ triplet of Higgs is introduced for each up-quark and down-quark sectors, respectively. The model has six real parameters and two complex parameters in addition to the modulus $τ$. By inputting six quark masses and three CKM mixing angles, we can predict the CP violation phase $δ$ and the Jarlskog invariant $J_{CP}$. The predicted ranges of $δ$ and $J_{CP}$ are consistent with the observed values. The absolute value of $V_{ub}$ is smaller than $0.0043$, while $V_{cb}$ is lager than $0.0436$. In conclusion, our quark mass matrices with the $A_4$ modular symmetry can reproduce the CKM mixing matrix completely with observed quark masses.

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arXiv2019

Dark Matter, Muon $g-2$, Electric Dipole Moments and $Z\to \ell_i^+ \ell_j^-$ in a One-Loop Induced Neutrino Model

We study a simple one-loop induced neutrino mass model that contains both bosonic and fermionic dark matter candidates and has the capacity to explain the muon anomalous magnetic moment anomaly. We perform a comprehensive analysis by taking into account the relevant constraints of charged lepton flavor violation, electric dipole moments, and neutrino oscillation data. We examine the constraints from lepton flavor-changing $Z$ boson decays at one-loop level, particularly when the involved couplings contribute to the muon $g-2$. It is found that $\text{BR}(Z\to μτ)\simeq (10^{-7}$ - $10^{-6})$ while $\text{BR}(τ\toμγ)\lesssim 10^{-11}$ in the fermionic dark matter scenario. The former can be probed by the precision measurement of the $Z$ boson at future lepton colliders.

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arXiv2018

A model with flavor-dependent gauged $U(1)_{B-L_1}\times U(1)_{B-L_2-L_3}$ symmetry

We propose a new model with flavor-dependent gauged $U(1)_{B-L_1}\times U(1)_{B-L_{2}-L_{3}}$ symmetry in addition to the flavor-blind one in the standard model. The model contains three right-handed neutrinos to cancel gauge anomalies and several Higgses to construct the measured fermion masses. We show the generic feature of the model and explore its phenomenology. In particular, we discuss the current bounds on the extra gauge bosons from the K and B meson mixings as well as the LEP and LHC data and focus on their contributions to the lepton flavor violating processes of $\ell_{i+1}\to \ell_iγ$ (i=1,2).

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arXiv2018

Predictive neutrino mass textures with origin of flavor symmetries

We investigate origins of predictive one-zero neutrino mass textures in a systematic way. Here we search Abelian continuous(discrete) global symmetries, and non-Abelian discrete symmetries, and show how to realize these neutrino masses. Then we propose a concrete model involving a dark matter candidate and an extra gauge boson, and show their phenomenologies.

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arXiv2018

An inverse seesaw model with $U(1)_R$ gauge symmetry

We propose a natural realization of inverse seesaw model with right-handed and flavor dependent $U(1)$ gauge symmetries, in which we formulate the neutrino mass matrix to reproduce current neutrino oscillation data in a general way. Also we study a possibility to provide predictions to the neutrino sector by imposing an additional flavor dependent $U(1)_{L_μ-L_τ}$ gauge symmetry that also satisfies the gauge anomaly cancellation conditions associated with $U(1)_R$. Then we analyze collider physics on a extra gauge boson and show a possibility of detection.

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arXiv2018

Neutrino mass generation with large $SU(2)_L$ multiplets under local $U(1)_{L_μ- L_τ}$ symmetry

We propose a model of neutrino mass matrix with large $SU(2)$ multiplets and gauged $U(1)_{L_μ- L_τ}$ symmetry, in which we introduce $SU(2)$ quartet scalar and quintet fermions with nonzero $L_μ- L_τ$ charge. Then we investigate the neutrino mass structure and explore phenomenologies of large multiplet fields at the collider, particularly, focussing on doubly- and singly- charged exotic leptons from the quintet.

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arXiv2018

A predictive model of radiative neutrino mass with gauged $U(1)_{B-2L_{\ell_2}-L_{\ell_1}}$ symmetry

We propose a predictively radiative neutrino mass model with gauged $U(1)_{B-2L_{\ell_2}-L_{\ell_1}}$ symmetry in which we successfully realize two-zero textures of neutrino mass matrix depending on charge assignment for leptons and the singlet scalar fields. Then some correlations of neutrino parameters are shown where we take mass structure given by $(\ell_2, \ell_1) = (μ, τ)$ or $(μ, e)$ as a representative case. Furthermore we discuss phenomenology of the model such as lepton flavor violations, collider physics, and dark matter candidate.

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arXiv2018

Zee-Babu type model with $U(1)_{L_μ- L_τ}$ gauge symmetry

We extend the Zee-Babu model introducing local $U(1)_{L_μ- L_τ}$ symmetry with several singly-charged bosons. We find a predictive neutrino mass texture in a simple hypothesis that mixings among singly-charged bosons are negligible. Also lepton flavor violations are less constrained compared with the original model. Then we explore testability of the model focussing on a doubly-charged boson physics at the LHC and the ILC.

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arXiv2018

A model with isospin doublet $U(1)_D$ gauge symmetry

We propose a model with an extra isospin doublet $U(1)_D$ gauge symmetry, in which we introduce several extra fermions with odd parity under a discrete $Z_2$ symmetry in order to cancel the gauge anomalies out. A remarkable issue is that we impose nonzero $U(1)_D$ charge to the standard model Higgs, and it gives the most stringent constraint to the vacuum expectation value of a scalar field breaking the $U(1)_D$ symmetry that are severer than the LEP bound. We then explore relic density of a Majorana dark matter candidate without conflict of constraints from lepton flavor violating processes. A global analysis is carried out to search for parameters which can accommodate with observed data.

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arXiv2018

Hidden $U(1)$ gauge symmetry realizing a neutrinophilic two-Higgs-doublet model with dark matter

We propose a neutrinophilic two Higgs doublet model with hidden local $U(1)$ symmetry, where active neutrinos are Dirac type, and a fermionic DM candidate is naturally induced as a result of remnant symmetry even after the spontaneous symmetry breaking. In addition, a physical Goldstone boson is arisen as a consequence of two types of gauge singlet bosons and contributes to the DM phenomenologies as well as additional neutral gauge boson. Then we will analyze the relic density of DM within the safe range of direct detection searches, and show the allowed region of dark matter mass.

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arXiv2018

A radiative seesaw model with higher order terms under an alternative $U(1)_{B-L}$

We propose a model based on an alternative $U(1)_{B-L}$ gauge symmetry with 5 dimensional operators in the Lagrangian, and we construct the neutrino masses at one-loop level, and discuss lepton flavor violations, dark matter, and the effective number of neutrino species due to two massless particles in our model. Then we search allowed region to satisfy the current experimental data of neutrino oscillation and lepton flavor violations without conflict of several constraints such as stability of dark matter and the effective number of neutrino species, depending on normal hierarchy and inverted one.

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