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Hiroshi Okada

Publications and source records attributed to Hiroshi Okada.

At least 55 records · Page 3Linked to original sources
arXiv2024

Muon $g-2$, dark matter, and neutrino mass explanations in a modular $A_4$ symmetry

We study a successful model to explain the muon anomalous magnetic moment originating from Yukawa-type interactions {in a supersymmetric theory}. Thanks to a modular $A_4$ flavor symmetry, any lepton flavor violations that spoil the model are forbidden. We also investigate a predictive radiative seesaw model including a dark matter (DM) candidate. At first, we construct the minimum model to satisfy the neutrino oscillation data and obtain several predictions such as Dirac CP and Majorana phases, the neutrino masses through $χ^2$ analysis. However, the minimum model would not provide our promising DM candidate. Thus, we minimally extend the model and find a good DM candidate. In the extended framework, we show the allowed regions to satisfy the muon anomalous magnetic moment and the observed relic density of dark matter in addition to predictions of the lepton sector.

hep-ph↗
arXiv2024

Electroweak phase transition with radiative symmetry breaking in Type-II seesaw with inert doublet

We consider the Type-II seesaw model extended with another Higgs doublet, which is odd under the $Z_2$ symmetry. We look for the possibility of triggering the electroweak symmetry breaking via radiative effects. The Higgs mass parameter changes sign from being positive at higher energy scales to negative at lower energy scales in the presence of the TeV scalar triplet. The Planck scale perturbativity is demanded and the electroweak phase transition is studied using two-loop $β$-functions. The maximum allowed values for the interaction quartic coupling of the second doublet field and the triplet field with the Higgs field are $λ_3=0.15$ and $λ_{Φ_{1Δ}}=0.50$, respectively. Considering these EW values, the first-order phase transition, i.e., $ϕ_{+}(T_c)/T_c\sim 0.6$ is satisfied only for vanishing doublet and triplet bare mass parameters, $m_{Φ_2}=0.0$ GeV and $m_Δ=0.0$ GeV. The small non-zero induced vacuum expectation value for the scalar triplet also generates the neutrino mass, and the lightest stable neutral particle from the inert doublet satisfies the dark matter constraints for the chosen parameter space. The impact of the thermal corrections on the stability of the electroweak vacuum is also studied, and the current experimental values of the Higgs mass and the top mass lie in the stable region both at the zero temperature and the finite temperature.

hep-ph↗
arXiv2023

Flavor, CP and Metaplectic Modular Symmetries in Type IIB Chiral Flux Vacua

We examine symmetries of chiral four-dimensional vacua of Type IIB flux compactifications with vanishing superpotential $W=0$. We find that the ${\cal N}=1$ supersymmetric MSSM-like and Pati-Salam vacua possess enhanced discrete symmetries in the effective action below the mass scale of stabilized complex structure moduli and dilaton. Furthermore, a generation number of quarks/leptons is small on these vacua where the flavor, CP and metaplectic modular symmetries are described in the framework of eclectic flavor symmetry.

hep-th↗
arXiv2023

Novel moduli space in modular flavor models : a case study for modular $T'$ seesaw model with hidden $SU(2)$ gauge symmetry

We study flavor phenomenologies in a basis of a double covering of modular $A_4$ group with a hidden $SU(2)$ symmetry, in which we work on regions at nearby two fixed points and three special points. These special points of $SL(2,\mathbb{Z})$ moduli space are statistically favored in flux compactifications of Type IIB string theory. Neutrino masses are approximately obtained by using the seesaw mechanism due to our two additional symmetries. We perform chi square numerical analysis for each of the fixed/special points in the normal and inverted hierarchies and demonstrate predictions for each case. Then, we briefly discuss the possible signature of hidden gauge bosons at collider experiments from the hidden $SU(2)$ symmetry.

hep-ph↗
arXiv2023

Modular flavor models with positive modular weights: a new lepton model building

We propose an interesting assignment of positive modular wights for fields in a modular non-Abelian discrete flavor symmetry. By this assignment, we can construct inverse seesaw and linear seesaw models without any additional symmetries which possess good testability in current experiments. At first, we discuss probabilities for positive modular wights from a theoretical point of view. Then we show concrete examples of inverse seesaw and linear seesaw scenarios applying modular $A_4$ symmetry as examples and demonstrate some predictions as well as being consistent with experimental results such as their masses and mixings.

hep-ph↗
arXiv2023

Neutrinophilic DM annihilation in a model with $U(1)_{L_μ-L_τ} \times U(1)_{H}$ gauge symmetry

We propose a model with two different extra $U(1)$ gauge symmetries; muon minus tauon symmetry $U(1)_{{L_μ}-L_τ}$ and hidden symmetry $U(1)_H$. Then, we explain muon anomalous magnetic moment, semi-leptonic decays $b\to s\ell\bar\ell$, and dark matter. In particular, we find an intriguing dark matter candidate to be verified by Hyper-Kamiokande and JUNO in the future that request neutrinophilic DM with rather light dark matter mass$\sim{\cal O}(10)$ MeV.

hep-ph↗
arXiv2023

Exploring CP-violation in $Y=0$ inert triplet with real singlet

In this article, we examine the Standard Model extended with a $Y=0$ Higgs triplet and a real singlet. We consider the Higgs triplet to be odd under the $Z_2$ symmetry, and hence the lightest stable particle from the inert triplet becomes the dark matter candidate, whereas the real singlet is considered to be even under the $Z_2$ symmetry. A dimension-5 effective term is introduced with the help of a real singlet, which breaks the CP symmetry and gives an additional source of CP-violation in the fermion sector. The phase transition proceeds in two-steps, with the symmetry breaking in the singlet direction occurring first and later leading to the usual electroweak symmetry breaking minima, while electroweak baryogenesis is associated with the second step. The parameters chosen for the electroweak phase transition are found to be consistent with the Planck scale stability and the perturbativity using two-loop $β$-functions. The DM mass bound for inert triplet, i.e., 1.2 TeV (below which it is under abundance), also comes out to be consistent with the strongly first-order phase transition, which was not possible solely with inert triplet. The upper bound on the triplet mass comes out to be $\leq 3.8$ TeV, which satisfies the strongly first-order phase transition. This particular benchmark point also satisfies the correct baryon asymmetry of the Universe $(6.13 \times 10^{-11})$, and the gravitational wave spectrum also lies within the detectable frequency range of LISA $(6.978 \times 10^{-4} - 1.690 \times 10^{-2} )$ Hz and BBO $(2.80\times 10^{-3}-1.096)$ Hz experiments.

hep-ph↗
arXiv2023

Texture zeros realization in a three-loop radiative neutrino mass model from modular $A_4$ symmetry

We derive verifiable two-zero textures in the framework of a three-loop induced neutrino mass model applying a modular $A_4$ symmetry for the lepton sector. Interestingly, the neutrino mass structure is determined by assignments of the right-handed charged-lepton particles only. We show all the possible texture patterns and demonstrate their analytical and numerical analyses. Finally, we mention a possibility of detection for doubly-charged boson via colliders that decays into specific modes due to the flavor symmetry.

hep-ph↗
arXiv2023

A model explaining the new CDF II W boson mass linking to muon $g-2$ and dark matter

We propose a model to explain the W boson mass anomaly reported by the CDFII collaboration that would suggest new physics (NP). We introduce exotic fermions; one isospin doublet vector-like lepton, one isospin singlet singly-charged vector-like lepton, and an isospin doublet inert scalar. The proposed model provides sizable muon anomalous magnetic moment (muon $g-2$) due to no chiral suppression and nonzero mass difference between the real and imaginary parts of neutral inert scalar bosons. The inert scalar mass squared difference and vector-like exotic leptons ($L', E'$ in the main text) affect oblique parameters. Especially, the $T$-parameter shift from zero explains the W boson mass anomaly. We search for the allowed parameter region to explain both muon $g-2$ and W boson mass anomaly at the same time. We also discuss a dark matter (DM) candidate assuming the real part of the inert scalar field to be the one. We find that lighter DM mass is favored to be consistent with experimental constraints.

hep-ph↗
arXiv2023

Quark and lepton model with flavor specific dark matter and muon $g-2$ in modular $A_4$ and hidden $U(1)$ symmetries

We propose a quark and lepton model explaining their masses, mixings, and CP violating phases, introducing modular $A_4$ and hidden gauged $U(1)$ symmetries. The hidden $U(1)$ brings us heavier Majorana fermions that are requested by chiral anomaly cancellations, and we work on a canonical seesaw scenario due to their neutral particles.In this framework, we search for favorite parameter space to satisfy both the experimental values and show predictions, applying the $χ$ square analysis.Then, we discuss a bosonic dark matter candidate that only annihilates into muon state due to the modular $A_4$ flavor symmetry where we suppose the main interaction of dark matter to be Yukawa terms. And we study muon anomalous magnetic dipole moment where there are not any constraints of lepton flavor violations thanks to this flavor symmetry. Finally, we show the allowed space to satisfy the observed relic density of dark matter and the muon anomalous magnetic dipole moment.

hep-ph↗
arXiv2023

Scotogenic models with a general lepton flavor dependent $U(1)$ gauge symmetry

We discuss radiative neutrino mass models with a general lepton flavor dependent $U(1)$ gauge symmetry. The scotogenic model is adopted for neutrino mass generation in which $Z_2$ odd singlet fermions and an inert scalar doublet are introduced. A lepton flavor dependent local $U(1)$ symmetry is applied to realize two-zero texture of a Majorana mass matrix of $Z_2$ odd singlet fermions where we explore minimal construction choosing $U(1)$ charges of the standard model fermions and singlet fermions. Then we investigate neutrino mass matrix and show some predictions for constructed models, and discuss some phenomenological implications.

hep-ph↗
arXiv2023

Fermi-LAT GeV excess and muon $g-2$ in a modular $A_4$ symmetry

The recent measurement of muon anomalous magnetic dipole moment (muon $g-2$) suggests that there might exist new physics that dominantly interacts with muons. The observed gamma-ray excess from Fermi-LAT indicates that dark matter annihilates into a specific charged fermions. We propose a successful model simultaneously to explain the Fermi-LAT GeV gamma-ray excess and sizable muon $g-2$ with a modular $A_4$ symmetry. Due to nature of this symmetry, our DM only interacts with pairs of muon and we explain sizable muon $g-2$ without suffering from constraints of any lepton flavor violations. We numerically show our allowed spaces on each measurements of Fermi-LAT, relic density of DM and muon $g-2$, randomly scanning our input parameters.

hep-ph↗
arXiv2023

A hidden gauged $U(1)$ addressing radiative neutrino mass, dark matter, $(g-2)_μ$, and $H_0$ tension

We propose a radiative seesaw model with a hidden $U(1)$ gauge symmetry. In order to have anomaly cancellations, we need to introduce several new fermions that contribute to muon anomalous magnetic dipole moment $(g-2)_μ$ as well as explain the neutrino oscillation data. We also consider a fermionic dark matter candidate that correlates with $(g-2)_μ$ and neutrino mass matrix at the same time. We show allowed regions in our input parameters satisfying several constraints. Finally, we also briefly discuss the possibility of the resolution of the Hubble tension via neutrino self-interactions mediated by a lighter hidden gauge boson without spoiling our model.

hep-ph↗
arXiv2023

$SU(4)_C \times SU(2)_L \times U(1)_R$ models with modular $A_4$ symmetry

We study $SU(4)_C \times SU(2)_L \times U(1)_R$ models with modular $A_4$ symmetry that provide unified description of the quark and lepton sector including the flavor structures. The models are distinguished by the assignments of the modular weight on matter superfields. We carry out numerical $χ^2$ analysis and search for parameter sets that accomodate the experimental results. We provide a benchmark point for each model to illustrate implications of our models.

hep-ph↗
arXiv2022

Phenomenological implications on a hidden sector from the Festina Lente bound

We apply the Festina Lente (FL) bound on a hidden sector with $U(1)$ gauge symmetries. Since the FL bound puts a lower bound on masses of particles charged under the $U(1)$ gauge symmetries, it is possible to constrain the hidden sector even with a tiny coupling to the Standard Model. In particular, we focus on the phenomenological implications of the FL bound on milli-charged particles, which naturally arise when kinetic mixing between the photon and the hidden photon is allowed. It turns out that the milli-charged particle with the mass $M\lesssim 5$ meV is prohibited by the FL bound in the case of a single hidden $U(1)$, independent of the value of kinetic mixing. This bound is crucial when bosonic dark matter is taken in consideration in this framework: the fuzzy bosonic dark matter models requesting minuscule masses are ruled out by the FL bound if the longevity of dark matter is protected by the hidden gauge symmetry.

hep-ph↗
arXiv2022

Towards unification of lepton and quark mass matrices from double covering of modular $A_4$ flavor symmetry

We study quark and lepton masses and mixings in a double covering of modular $A_4$ flavor symmetry in which we search for common solution of a single modulus $τ$, applying chi-square numerical analysis under the as minimum framework as possible. We have found the common region of $τ$ within $5σ$ interval that is narrow in case of normal hierarchy, but not found in case of inverted hierarchy.

hep-ph↗
arXiv2022

An alternative gauged $U(1)_R$ symmetric model in light of the CDF II $W$ boson mass anomaly

We consider an explanation of CDF II W bosom mass anomaly by $Z-Z'$ mixing with $U(1)_R$ gauge symmetry under which right-handed fermions are charged. It is found that $U(1)_R$ is preferred to be leptophobic to accommodate the anomaly while avoiding other experimental constraints. In such a case we require extra charged leptons to cancel quantum anomalies and the SM charged leptons get masses via interactions with the extra ones. These interactions also induce muon $g-2$ and lepton flavor violations. We discuss muon $g-2$, possible flavor constraints, neutrino mass generation via inverse seesaw mechanism, and collider physics regarding $Z'$ production for parameter space explaining the W boson mass anomaly.

hep-ph↗
arXiv2022

Residual flavor symmetry breaking in the landscape of modular flavor models

We study a symmetry breaking of residual flavor symmetries realized at fixed points of the moduli space. In the supersymmetric modular invariant theories, a small departure of the modulus from fixed points is required to realize fermion mass hierarchies and sizable CP-breaking effects. We investigate whether one can dynamically fix the moduli values in the vicinity of the fixed points in the context of Type IIB string theory. It is found that the string landscape prefers $|δτ| \simeq 10^{-5}$ for the deviation of the complex structure modulus from all fixed points and the CP-breaking vacuum is statistically favored. To illustrate phenomenological implications of distributions of moduli values around fixed points, we analyze the lepton sector on a concrete $A_4$ modular flavor model.

hep-ph↗