arXiv subjects

Hiroshi Okada

Publications and source records attributed to Hiroshi Okada.

At least 37 records · Page 2Linked to original sources

arXiv2025

Radiative inverse seesaw model with hidden $U(1)$ gauge symmetry enhancing lepton $g-2$

We propose a new inverse seesaw model based on hidden local $U(1)$ symmetry framework where inverse seesaw mechanism is induced at one loop level. A Majorana mass term of singlet fermion is forbidden by the $U(1)$ symmetry and it is generated at one-loop level by introducing relevant particle contents to get loop diagram, inducing inverse seesaw mechanism. The same particle contents also contribute to lepton magnetic(electric) dipole moment and lepton flavor violating decays without chiral suppression. We can then obtain sizable muon anomalous magnetic dipole moment that accommodate with deviation from the standard model prediction. The constraints from lepton flavor violating decays and electron magnetic(electric) dipole moment are also discussed to explore testability of the model.

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arXiv2025

Neutrino mass model at a three-loop level from a non-holomorphic modular $A_4$ symmetry

We study a three-loop induced neutrino mass scenario from a non-holomorphic modular $A_4$ flavor symmetry and reach the minimum scenario leading predictions of the lepton masses, mixing angles, and Dirac and Majorana phases, which are shown through the chi square analyses. In addition, we discuss the lepton flavor violations, muon anomalous magnetic moment, lepton universality, and relic density of the dark matter candidate. And, we find that we need to extend our model if we satisfy the observed relic density of dark matter within the limit of perturbation where it can be done by adding one singlet scalar boson without changing predictions in neutrino sector.

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arXiv2025

A radiative seesaw model in a non-invertible selection rule with the assistance of a non-holomorphic modular $A_4$ symmetry

We propose a two-loop neutrino mass model where fermionic and bosonic dark matter (DM) candidates are simultaneously connected to the neutrinos. But the fermionic DM candidate is favored compared to the bosonic one due to generating the fermionic DM mass at one-loop level. In order to obtain our desired Lagrangian and Higgs potential, we introduce a $Z_3$ gauging TY non-invertible fusion rule with the assistance of a non-holomorphic modular $A_4$ symmetry. The fusion rule forbids the mass of DM candidate at tree level but its mass is generated at one-loop level where the DM mass term dynamically violates the fusion rule. After that, the neutrino mass matrix is induced at one-loop level where a remnant $Z_2$ symmetry is still remained. The symmetry assures the stability of our DM candidate. The non-holomorphic modular $A_4$ symmetry plays a role in forbidding the interactions between the SM particles and heavier fermions $X_R$ and an isospin singlet inert scalar boson $S_0$ that run in the DM mass loop, in addition to reduction our free parameters that leads to our predictions for lepton sector. We perform $χ^2$ numerical analysis for the lepton masses, mixing angles, and phases, and we show several predictions for NH and IH. Then, we demonstrate our lepton flavor violations, muon anomalous magnetic dipole moment, and the relic density of the DM candidate fixing the best fit point of the lepton sector.

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arXiv2025

A natural realization of inverse seesaw model in a non-invertible selection rule

We propose natural hierarchies among neutral fermions in a framework of inverse seesaw, imposing a $Z_3$ Tambara-Yamagami fusion rule which is applied to our phenomenology. Under the symmetry, the Majorana mass terms for $N_R$ and $N_L$ are forbidden at tree level. However they are generated at one-loop level where the symmetry is dynamically broken. In order to realize such loop corrections, we introduce neutral boson and fermion either of which can be an appropriate dark matter candidate. Finally, we show the best fit value of the neutrino sector for normal and inverted hierarchies referring recent experimental results.

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arXiv2025

Neutrino Masses and Mixing in an Axion Model

We propose a novel framework that simultaneously addresses three critical issues: tiny neutrino masses and their mixing patterns, dark matter, and the strong CP problem. Our model extends the Peccei-Quinn (PQ) symmetry by incorporating modular $S_3$ symmetry, which plays a central role in explaining the observed neutrino mixing structure. The field content includes two vector-like colored fermions and three colored scalars as $S_3$ singlets, an isospin doublet inert scalar and a singlet PQ scalar, each assigned appropriate modular weights. We show that such an extension, together with a suitable assignment of modular weights to the fields, can lead to holomorphic modular forms of Yukawa interactions, which can be derived from a superpotential. Furthermore, we explore an extension of the model to include non-holomorphic Yukawa interactions in the non-supersymmetric framework and show that the results are distinct from the holomorphic case. Tiny neutrino masses are generated radiatively through colored mediators, while the KSVZ-type axion appears to dynamically resolve the strong CP problem. We investigate the phenomenology of lepton flavor violation and the muon $g-2$ anomaly within this framework. Additionally, we explore the axion's properties and its role as dark matter.

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arXiv2025

Three-loop induced neutrino mass model in a non-invertible symmetry

We propose a new type of radiatively induced neutrino masses at three-loop level based on the Ma model, introducing a non-invertible symmetry in the class under a ${\mathbb Z_2}$ gauging of ${\mathbb Z_6}$ symmetry and adding three isospin doublet vector-like fermions $L'$ and singlet boson $S_0$. Under this symmetry, the Yukawa interactions directly related to the neutrino masses are not allowed at tree-level. However it is allowed at one-loop level due to $L'$ and $S_0$ as well as $η$, which is no longer invariant under this symmetry. Therefore, the symmetry is dynamically broken. Intriguingly, $η$ plays important roles in contributing to both the radiative matrices $y^η$ and $m_ν$. After constructing our model, we show some numerical analyses to satisfy the lepton flavor violations, muon anomalous magnetic dipole moment, and a boson dark matter candidate $S_0$ or $η_R$ for the cases of normal hierarchy and inverted hierarchy. Then, we demonstrate allowed space for our input parameters.

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arXiv2025

A radiative lepton model in a non-invertible fusion rule

We propose a new mechanism in which electron and muon masses are induced at one-loop level after dynamically violating the symmetry of the Ising fusion rule. In the neutrino sector, while the neutrino mass is generated at one-loop level, the Ising fusion rule plays a role in stabilizing the particles inside the loop. As a result, the symmetry works like a $Z_2$ symmetry that is not broken at any loop order. Subsequently, we discuss the lepton flavor violating processes, muon anomalous magnetic dipole moment, and relic density of dark matter, where we specify our dark matter candidate to be a singlet boson and briefly analyze the relic density by estimating the DM annihilation cross section. Finally, we present results for both the DM cross section and the muon $g-2$, satisfying the neutrino oscillation data as well as the constraints of lepton flavor violations.

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arXiv2025

A new type of lepton seesaw model in a modular $A_4$ symmetry

We propose a new type of lepton seesaw model introducing a modular $A_4$ flavor symmetry in which isospin doublet vector fermions play an important role in constructing seesaw mechanisms for both the charged-lepton mass matrix and the neutrino one. The charged-lepton mass matrix is induced via the Dirac seesaw with a two-by-two block mass matrix. On the other hand, the neutrino mass matrix is generated via a seesaw with four-by-four block mass matrix where the right-handed neutral fermions are also added. Remarkably the neutral fermion mass matrix provides us a new type of seesaw formula for active neutrino mass. Through our chi square analysis, we find some tendencies about observables focusing on two fixed points $τ=i,\ ω$.

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arXiv2025

Radiative lepton seesaw model in a non-invertible fusion rule and gauged $B-L$ symmetry

We propose a radiative lepton seesaw model with the ${\mathbb Z}_3$ Tambara-Yamagami fusion rule and gauged $B-L$ symmetry. The heavier right-handed neutral fermions ($N_R$) simultaneously contribute to the masses of charged-leptons and neutrinos, and three families of $N_R$ are necessary in realizing realistic mass matrices. On the other hand, we introduce a gauged $B-L$ symmetry to preserve the lepton seesaw mechanism. As a result, this gauged symmetry not only assures the three families of $N_R$ from view point of chiral gauge anomaly cancellation, but also provides a dominant annihilation cross section via Higgs portal in order to explain the correct relic density of dark matter. Finally, we show several numerical results satisfying the neutrino oscillation data, lepton flavor violations, muon $g-2$, and relic density of dark matter.

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arXiv2025

Zee model in a non-holomorphic modular $A_4$ symmetry

We study a Zee model in a non-holomorphic modular $A_4$ flavor symmetry in which we find good predictions in both the cases of normal and inverted hierarchy. Parameter reduction on neutrino sector occurs due to large mass hierarchies between charged-leptons mass eigenvalues and new singly-charged bosons in addition to this flavor symmetry. As a result, we have two complex free parameters including modulus $τ$. We show several predictions in terms of verifiable observables such as Dirac CP, Majorana phases, sum of the neutrino masses, and the effective mass for neutrino double beta decay in addition to demonstrating allowed regions for our input parameters.

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arXiv2025

A radiative neutrino mass model with leptoquarks under non-holomorphic modular $A_4$ symmetry

We investigate a radiative seesaw model with two leptoquarks under non-holomorphic modular $A_4$ symmetry. The leptons and quarks belong to non-trivial representations of the modular $A_4$ and the structures of their mass matrices are restricted. Neutrino masses are generated at one-loop level via leptoquark inside loop diagram where structures of relevant Yukawa interactions are determined by the modular $A_4$ symmetry. We scan the free parameters in the model and try to fit all the observed data for both lepton and quark sectors. For allowed parameters, we show some predictions regarding neutrino observables such as sum of neutrino mass and neutrinoless double beta decay.

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arXiv2025

Type-II seesaw of a non-holomorphic modular $A_4$ symmetry

We search for predictability of lepton masses and mixing patterns of type-II seesaw scenario in a non-holomorphic modular $A_4$ symmetry recently proposed by Qu and Ding. We propose three types of minimum predictive models with different assignments of modular weight, satisfying the neutrino oscillation data in Nufit 5.2. The cosmological bound on the sum of neutrino mass is stringent to our models and CMB bound $\sum D_ν\le0.12$ eV can be satisfied by one of three models playing an important role in discriminating them.

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arXiv2025

Zee model in a modular $A_4$ symmetry

We study a Zee model applying a modular $A_4$ symmetry in supersymmetry framework, where we construct our lepton model as minimum modular weight as possible. We show our predictions on phases and neutrino masses through numerical analysis. We find a model that can fit in both normal and inverted hierarchy cases of neutrino mass. The predictions of neutrino observables are shown where we obtain more constrained allowed region in the inverted hierarchy case.

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arXiv2025

Muon $g-2$ with $SU(2)_L$ multiplets

We propose a simple model to obtain sizable muon anomalous magnetic dipole moment (muon $g-2$) introducing several $SU(2)_L$ multiplet fields without any additional symmetries. The neutrino mass matrix is simply induced via type-II seesaw scenario in terms of $SU(2)_L$ triplet Higgs with $U(1)_Y$ hypercharge 1. In addition, we introduce an $SU(2)_L$ quartet vector fermion with $1/2$ hypercharge and scalar with $3/2$ hypercharge. The quartet fermion plays a crucial role in explaining muon $g-2$ causing the chiral flip inside a loop diagram with mixing between triplet and quartet scalar bosons via the standard model Higgs. We show numerical analysis and search for allowed region in our parameter space, and demonstrate the collider physics.

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arXiv2025

A radiative seesaw in a non-holomorphic modular $S_3$ flavor symmetry

We study a non-holomorphic modular $S_3$ flavor symmetry in which we analyze neutrino sector, dark matter, and lepton flavor violations. The active neutrino mass is generated via one-loop level. We achieve chi-square analysis and demonstrate some predictions in cases of normal hierarchy with fermionic or bosonic dark matter and inverted hierarchy of fermionic or bosonic dark matter.

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arXiv2024

A more novel approach of radiative linear seesaw in a modular $A_4$ symmetry

We propose a radiatively induced linear seesaw model that is perfectly realized at leading order by a modular $A_4$ symmetry. Because this group also has a flavor symmetry, we obtain some predictions concentrating on two specific regions at nearby fixed points $τ=ω$ and $i$. Through our numerical chi square analysis, we show predictions for each the case depending on the neutrino mass ordering; normal and inverted one.

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arXiv2024

Non-Holomorphic Modular $\mathcal{A}_4$ Symmetric Scotogenic Model

The present work extends scotogenic and its modular $\mathcal{A}_4$ variation a step forward and demonstrates scotogenic modular $\mathcal{A}_4$ non-supersymmetric realization. To achieve this non-holomorphic modular symmetries come to rescue. Advantage of the current construction is the compactness of the model content and absence of the supersymmetric fields. Neutrino mass is generated through a canonical scotogenic mechanism. The allowed values of the VEV of the $τ$ modulus are $τ\simeq w$ and Im$[τ]\approx 2$. The non-holomorphic modular $\mathcal{A}_4$ symmetry leads to correlations among the neutrino observables.

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arXiv2024

Neutrino Mass Model and Dark Matter with $Y=0$ Inert Triplet Scalar

We study a one-loop induced neutrino mass model with an inert isospin triplet scalar field of $Y=0$ and heavier isospin doublet vector-like leptons and singlet Majorana right-handed fermions. In addition to the neutrino mass matrix, We explain sizable scale of muon anomalous magnetic dipole moment $10^{-9}$ by introducing a singly-charged boson $S^\pm$. We show numerical analysis of neutrino oscillation, lepton flavor violations, Z boson decays, and demonstrate our allowed regions in cases of normal and inverted hierarchies. We find the sizable scale of muon anomalous magnetic dipole moment for both cases. Then, we move on to the discussion of dark matter candidates to satisfy the relic density where we have two candidates; fermionic dark matter and bosonic one. And, we classify four cases fermionic dark matter with normal and inverted hierarchies, bosonic one with normal and inverted hierarchies and search for each of the allowed points in the model.

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