arXiv subjects

Takaaki Nomura

Publications and source records attributed to Takaaki Nomura.

At least 37 records · Page 2Linked to original sources

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

Revisiting Flavor Model and Leptogenesis

We revisit a supersymmetric flavor model based on the symmetries $SU(2)_L \times A_4 \times Z_3 \times U(1)_R$, which extends the original Altarelli and Feruglio construction by introducing flavon and driving superfields responsible for the spontaneous breaking of the flavor symmetry in order to obtain non-zero reactor angle. The vacuum alignments of flavon fields are achieved through the minimization of the scalar potential derived from the superpotential. This setup leads to specific mass matrices for the charged leptons and neutrinos that are consistent with current experimental data, including the measured values of the lepton mixing angles and neutrino mass squared differences. We investigate whether the model can simultaneously accommodate successful thermal leptogenesis. In particular, we analyze the CP asymmetry generated in the decay of heavy Majorana neutrinos, the resulting lepton asymmetry, and its conversion to the baryon asymmetry through the electroweak sphalerons. However the CP asymmetry is zero, since the Dirac neutrino mass matrix is simple texture in the leading order for our model. Then we consider the next-to-leading order in Yukawa interactions of the Dirac neutrinos. Therefore, we can realize the baryon asymmetry of the universe at the present universe. By numerically scanning the parameter space, we identify the regions consistent with both neutrino oscillation data and the observed baryon asymmetry. In the specific case such that one of the couplings for the right-handed Majorana neutrinos is real parameter, the predicted lightest neutrino mass is at least $5$ meV and $15$ meV for the normal and inverted neutrino mass hierarchies, respectively. In addition, the range of the Majorana phases may be tested in future experiments.

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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

Directional Direct Detection of MeV Scale Boosted Dark Matter in Two Component Dark Matter Scenario via Dark Photon Interaction

This study explores a two-component dark matter model in which one component, heavier dark matter, annihilates into a lighter dark matter. The lighter dark matter is expected to generate detectable signals in detectors due to its enhanced momentum, enabling direct detection even for MeV-scale dark matter. We investigate the effectiveness of directional direct detections, especially the nuclear emulsion detector NEWSdm, in verifying these boosted dark matter particles through nuclear recoil. In particular, we focus on light nuclei, such as protons and carbon, as suitable targets for this detection method due to their high sensitivity to MeV-scale dark matter. By modeling the interactions mediated by a dark photon in a hidden U(1)$_D$ gauge symmetry framework, we calculate the expected dark matter flux and scattering rates for various detector configurations. Our results show that nuclear emulsions have the potential to yield distinct, direction-sensitive dark matter signals from the Galactic center, providing a new way to probe low-mass dark matter parameter spaces that evade conventional detection methods.

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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

Multi-Lepton Jets from Quadruple $Z'$ via the Higgs Decay at LHC

We investigate multi-lepton jet events from the decay of the 125 GeV Higgs boson ($h$) into quadruple new gauge bosons $(Z')$ at the LHC. Such an exotic decay is realized via the process of $h \to ϕϕ\to Z'Z'Z'Z'$ with new scalar boson $ϕ$ in models with an additional $U(1)$ gauge symmetry. Charged leptons coming from the $Z'$ decay tend to be observed as lepton-jets rather than isolated leptons when the masses of $Z'$ and $ϕ$ are smaller than ${\cal O}$(10) GeV, because of the highly-boosted effects. Performing the signal and background analyses, we find that the branching ratio of $h \to 4Z'$ is maximally constrained to be smaller than of order $10^{-6}$ ($10^{-7}$) by using the muonic-lepton jets assuming the integrated luminosity of 140 fb$^{-1}$ (3000 fb$^{-1}$) at LHC. For lighter $Z'$ ($< 2m_μ$), we can use the electronic-lepton jets instead of the muon-jets, by which the upper limit on the branching ratio is obtained to be of order $10^{-6}$-$10^{-5}$. These bounds can be converted into the constraint on model parameters such as a mixing angle between $h$ and $ϕ$. It is shown that stronger bounds on the mixing angle are obtained in the dark photon case as compared with the previous constraints given by flavor experiments and the Higgs decay $h \to Z'Z'$ in the mass range of $m_{Z'}\lesssim 10$ GeV.

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arXiv2025

Neutrino observables in gauged $U(1)_{L_α-L_β}$ models with two Higgs doublet and one singlet scalars

We discuss neutrino sector in models with two Higgs doublet and one singlet scalar fields under local $U(1)_{L_α- L_β}$ symmetry. A neutrino mass matrix is formulated for these models where the matrix is generated via type-I seesaw mechanism introducing right-handed neutrinos. The neutrino mass matrix has more degrees of freedom compared to minimal scenarios which have only one new scalar field, but its structure is still restricted by the symmetry. Then it is find that sum of neutrino mass can be lower than minimal scenarios and it is easier to satisfy observed constraints. In addition, we can fit neutrino data for $U(1)_{L_e - L_{μ(τ)}}$ cases which are disfavored in minimal models. Furthermore, some correlations among sum of neutrino mass and CP violating phases are still found although we have more free parameters.

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arXiv2024

Leptonic dipole operator with $Γ_2$ modular invariance in light of Muon $(g-2)_μ$

We have studied the leptonic EDM and the LFV decays relating with the recent data of anomalous magnetic moment of muon, $(g-2)_μ$ in the leptonic dipole operator. We have adopted the successful $Γ_2$ modular invariant model by Meloni-Parriciatu as the flavor symmetry of leptons. Suppose the anomaly of $(g-2)_μ$, $Δa_μ$ to be evidence of New Physics (NP), we have related it with the anomalous magnetic moment of the electron $Δa_e$, the electron EDM $d_e$ and the $μ\to e γ$ decay. We found that the NP contributions to $Δa_{e(μ)}$ are proportional to the lepton masses squared likewise the naive scaling $Δa_\ell \propto m^2_\ell$. The experimental constraint of $|d_e|$ is much tight compared with the one from the branching ratio $\mathcal{B} (μ\to e γ)$ in our framework. Supposing the phase of our model parameter $δ_α$ for the electron to be of order one, we have estimated the upper-bound of $\mathcal{B}(μ\to e γ)$, which is at most $10^{-21}-10^{-20}$. If some model parameters are real, leptonic EDMs vanish since the CP phase of the modular form due to modulus $τ$ does not contribute to the EDM. However, we can obtain $\mathcal{B} (μ\to e γ)\simeq 10^{-13}$ with non-vanishing $d_e$ in a specific case. The imaginary part of a parameter can lead to $d_e$ in the next-to-leading contribution. The predicted electron EDM is below $10^{-32}$e\,cm, while $\mathcal{B} (μ\to e γ)$ is close to the experimental upper-bound. The branching ratios of $τ\to eγ$ and $τ\to μγ$ are also discussed.

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arXiv2024

Probing chiral and flavored $Z^\prime$ from cosmic bursts through neutrino interactions

The origin of tiny neutrino mass is an unsolved puzzle leading to a variety of phenomenological aspects beyond the Standard Model (BSM). We consider $U(1)$ gauge extension of the Standard Model (SM) where so-called seesaw mechanism is incarnated with the help of thee generations of Majorana type right-handed neutrinos followed by the breaking of $U(1)$ and electroweak gauge symmetries providing anomaly free structure. In this framework, a neutral BSM gauge boson $Z^\prime$ is evolved. To explore the properties of its interactions we consider chiral (flavored) frameworks where $Z^\prime$ interactions depend on the handedness (generations) of the fermions. In this paper we focus on $Z^\prime-$neutrino interactions which could be probed from cosmic explosions. We consider $ν\overlineν \to e^+ e^-$ process which can energize gamma-ray burst (GRB221009A, so far the highest energy) through energy deposition. Hence estimating these rates we constrain $U(1)$ gauge coupling $(g_X)$ and $Z^\prime$ mass $(M_{Z^\prime})$ under Schwarzchild (Sc) and Hartle-Thorne (HT) scenarios. We also study $ν-$DM scattering through $Z^\prime$ to constrain $g_X-M_{Z^\prime}$ plane using IceCube data considering high energy neutrinos from cosmic blazar (TXS0506+056), active galaxy (NGC1068), the Cosmic Microwave Background (CMB) and the Lyman-$α$ data, respectively. Finally highlighting complementarity we compare our results with current and prospective bounds on $g_X-M_{Z^\prime}$ plane from scattering, beam-dump and $g-2$ experiments.

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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

Multi-$Z'$ signatures of spontaneously broken local $U(1)'$ symmetry

We discuss multi-$Z'$ signatures coming from decays of Higgs bosons in models with a spontaneously broken $U(1)'$ symmetry, which can be observed as "lepton jets" or multi-lepton final states depending on the mass range of new bosons. We consider anomaly-free $U(1)'$ models without introducing new fermions except for right-handed neutrinos, in which the Higgs sector is composed of an isospin doublet and a singlet fields with zero and non-zero $U(1)'$ charges, respectively. The multi-$Z'$ signatures can then be obtained via the decays of the discovered (extra) Higgs boson $h$ ($ϕ$), i.e., $h\to Z'Z'$, $ϕ\to Z'Z'$ and/or $h \to ϕϕ\to 4Z'$ as far as kinematically allowed. We give the upper limit on the branching ratios of $h$ into $Z'Z'$ and $4Z'$ from the current experimental data in each model. We also show the deviation in the $hhh$ coupling from the standard model prediction at one-loop level, and find that its amount is typically smaller than 1\%.

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arXiv2024

Extended Scotogenic Model of Neutrino Mass and Proton Decay

The current article presents an extension of the classical scotogenic neutrino mass paradigm, where the three issues in particle physics: dark matter, smallness of neutrino mass, and stability of the proton are interconnected. The scenario encompasses the neutrino mass as well as the proton decay as a consequence of an existence of the dark matter. The study successfully achieves the correlation between the naturally small neutrino masses and naturally long proton lifetime in the present paradigm. Furthermore, all relevant cosmological, collider, and flavor physics constraints are incorporated in the detailed analysis. The scotogenic fermionic dark matter with the mass in the range from $100$ GeV to $10$ TeV successfully satisfies all relevant constraints. The valid range of $2.51\times 10^{-5} < λ< 2\times 10^{-3}$ is obtained for the 2HDM $λ$ coupling. We give a brief discussion, as well as, outline some of the future prospects.

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arXiv2024

Flavino Dark Matter in a Non-Abelian Discrete Flavor Model

We study a relic density of the flavino dark matter in modified Altarelli and Feruglio $A_4$ model which is respecting the $SU(2)_L\times A_4\times Z_3\times U(1)_R$ symmetry. We calculate the Lagrangian from the superpotential in the model. In estimating relic density, we consider the relevant interactions from the Lagrangian that realize the vacuum expectation value alignments and charged lepton masses where we assume that the supersymmetry breaking effects are small for flavon sector. As a result, we find the degenerate masses between the lightest ``flavon'' and ``flavino'', and only two parameters in the potential determines the relic density. Then allowed parameter space of these parameters are estimated from relic density calculation taking a constraint from lepton flavor violation into account. We also briefly discuss other dark matter physics such as direct detection, indirect detection and collider search.

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