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Takaaki Nomura

Publications and source records attributed to Takaaki Nomura.

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

Constraining vector dark matter and dark photon with degenerate mass in a hidden local SU(2) model

We discuss degenerate vector dark matter and dark photon that are induced from hidden $SU(2)_H$ gauge sector where it is spontaneously broken by vacuum expectation value of $SU(2)_H$ doublet. Kinetic mixing between $SU(2)_H$ and $U(1)_Y$ gauge fields can be generated by introducing dimension six operator realizing dark photon interactions. In estimating relic density we focus on the process in which dark matter annihilates into dark photons, and search for the region of dark matter mass and gauge coupling realizing observed relic density. We then discuss constraints from dark photon physics, thermalization of dark sector and direct detection of dark matter. It is then found that constraints from direct detection experiments give us the strongest upper limits on the dark photon interactions.

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arXiv2024

Probing for chiral $Z^\prime$ gauge boson through scattering measurement experiments

Motivated by the observation of tiny neutrino mass can not be explained within the framework of Standard Model (SM), we consider extra gauge extended scenarios in which tiny neutrino masses are generated through seesaw mechanism. These scenarios are equipped with beyond the standard model (BSM) neutral gauge boson called $Z^\prime$ in the general $U(1)_X$ symmetry which is a linear combination of $U(1)_Y$ and $U(1)_{B-L}$. In this case, left and right handed fermions interact differently with the $Z^\prime$. The $Z^\prime$ gives rise to different processes involving neutrino-nucleon, neutrino-electron, electron-nucleus and electron-muon scattering processes. By comparing with proton, electron beam-dump experiments data, recast data from searches for the long-lived and dark photon at BaBaR, LHCb and CMS experiments, the electron and muon $g-2$ data, and the data of the dilepton and dijet searches at the LEP experiment, we derive bounds on the gauge coupling and the corresponding gauge boson mass for different $U(1)_X$ charges and evaluate the prospective limits from the future beam-dump scenarios at DUNE, FASER(2) and ILC. We conclude that large parameter regions could be probed by scattering, beam-dump and collider experiments in future.

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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.

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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.

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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.

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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.

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arXiv2023

Boosting indirect detection of a secluded dark matter sector

Dark Matter (DM) residing in a secluded sector with suppressed portal interaction could evade direct detections and collider searches. The indirect detections provide the most robust probe to this scenario. Depending on the structure of the dark sector, novel DM annihilation spectra are possible. The dark shower is a common phenomenon for particles in the dark sector which take part in strong interactions and are boosted. In terms of simplified two-component DM models with vector portal interaction and pseudoscalar portal interaction, we study the dark showering effects for DM indirect detection. In those models, the heavier DM component which dominates the relic density annihilates into boosted lighter species. Together with the large coupling through which the lighter DM annihilates away in the early universe, the showered spectra provide as the smoking gun for the DM existence. Considering bounds obtained by the AMS-02 positron data and Fermi-LAT measurement of gamma-ray from the dwarf galaxies, we find the dark shower could open a new region of sensitivity that can not be probed before.

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arXiv2023

Gauged $U(1)_X$ breaking as origin of neutrino masses, dark matter and leptogenesis at TeV scale

We propose a new mechanism which simultaneously explains tiny neutrino masses, stability of dark matter and baryon asymmetry of the Universe via leptogenesis due to the common origin: a spontaneous breaking of a $U(1)_X$ gauge symmetry at TeV scale. The $U(1)_X$ breaking provides small Majorana masses of vector-like leptons which generate small mass differences among them, and enhance their CP-violating decays via the resonant effect. Such CP-violation and lepton number violation turns out to be a sufficient amount of the observed baryon asymmetry through leptogenesis. The Majorana masses from the $U(1)_X$ breaking also induce radiative generation of masses for active neutrinos at one-loop level. Furthermore, a $Z_2$ symmetry appears as a remnant of the $U(1)_X$ breaking, which guarantees the stability of dark matter. We construct a simple renormalizable model to realize the above mechanism, and show a benchmark point which can explain observed neutrino oscillations, dark matter data and the baryon asymmetry at the same time.

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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.

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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.

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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.

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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.

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arXiv2023

Multi muon/anti-muon signals via productions of gauge and scalar bosons in a $U(1)_{L_μ-L_τ}$ model at muonic colliders

We discuss the discovery potential of a promising signals, $3 \times μ^+ μ^-$ at a $μ^+ μ^-$ collider and $μ^+ μ^+ μ^+ μ^+ μ^- μ^- $ at a $μ^+ μ^+$ collider, that are obtained via production of $Z'$ and a new scalar boson $ϕ$ in a spontaneously broken local $U(1)_{L_μ- L_τ}$ model. We consider the $Z'$ associated production from the process $μ^+ μ^- \to ϕZ'$ in addition to a muonphilic $Z'$ fusion process $μ^+ μ^\pm \to ϕμ^+ μ^\pm$. The scalar boson is associated with $U(1)_{L_μ- L_τ}$ symmetry breaking and dominantly decays into $Z' Z'$ mode. We carry out numerical simulation analysis for signal and background processes to estimate a discovery significance for different benchmark points. It is shown that our signal can be observed with integrated luminosity less than $\mathcal{O}(100)$ fb$^{-1}$ for both $μ^+ μ^-$ and $μ^+ μ^+$ colliders with more than 5-$σ$ significance.

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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.

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arXiv2022

Chiral $Z^\prime$ in FASER, FASER2, DUNE, and ILC beam dump experiments

The origin of neutrino mass is a big unsolved problem of the Standard Model (SM) that motivate us to consider beyond the SM (BSM) scenarios where SM-singlet right-handed neutrinos (RHNs) are introduced to explain the origin of the light neutrino masses through the seesaw mechanism. There is a variety of ways which could lead us to this goal and one of them is a general U$(1)$ extension of the SM. In this scenario, three SM-singlet RHNs are introduced to cancel the gauge and mixed gauge gravity anomalies. After anomaly cancellation, we notice that the left- and right-handed charged fermions are differently charged under the general U$(1)$ gauge group evolving a chiral scenario. After the breaking of the general U$(1)$ symmetry, a neutral BSM gauge boson $(Z^\prime)$ acquires mass and it is a free parameter. Such $Z^\prime$, being lighter than $5$ GeV, could be probed at the intensity and lifetime frontiers like FASER, FASER2, DUNE, and ILC beam dump experiments. The estimated bounds are needed to be compared with the existing bounds. We find that existing constraints from Orsay, Nomad, PS191, KEK, LSND, CHARM experiments, and cosmological scenario like SN1987A can be compared in our case once estimated for chiral scenarios. Finally, we compare the parameter spaces showing viable ones that could be probed by FASER, FASER2, DUNE, and ILC beam dump experiments and already excluded regions from Orsay, Nomad, PS191, KEK, LSND, CHARM, and SN1987A for a chiral scenario.

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arXiv2022

Scotogenic top-quark FCNC decays

Flavor-changing neutral current (FCNC) top-quark decays are highly suppressed due to the Glashow-Iliopoulos-Maiani mechanism in the standard model (SM). If $t\to q h, qV$ with $V=g,γ, Z$ are all induced via quantum loop levels, then we investigate the effect that can enhance the top-FCNC up to the sensitivity designed at the high-luminosity (HL) LHC. Inspired by the mechanism of the scotogenic neutrino mass, we extend the SM by including $Z_2$-odd colored fermions when a $Z_2$ discrete is imposed. The results show that by taking $BR(t\to u g) \lesssim 0.61 \times 10^{-4}$ recently measured by ATLAS as an input, $t\to q γ$ can be indirectly bounded to be $BR(t\to q γ)\lesssim 3.2 \times 10^{-6}$, which is below the expected sensitivity at the HL LHC. After taking potential constraints from various experiments into account, the obtained branching ratios for the loop-induced $t\to q h$ and $t\to qZ$ decays can be $O(10^{-4})$, which falls within the sensitivity at the HL LHC.

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arXiv2022

A multi-charged particle model with local $U(1)_{μ-τ}$ to explain muon $g-2$, flavor physics, and possible collider signature

We consider a model with multi-charged particles including vector-like fermions and a charged scalar under a local $U(1)_{μ- τ}$ symmetry. We search for allowed parameter region explaining muon anomalous magnetic moment (muon $g-2$) and $b \to s \ell^+ \ell^-$ anomalies, satisfying constraints from the lepton flavor violations, $Z$ boson decays, meson anti-meson mixing and collider experiments. Carrying out numerical analysis, we explore the typical size of the muon $g-2$ and Wilson coefficients to explain $b \to s \ell^+ \ell^-$ anomalies in our model when all other experimental constraints are satisfied. We then discuss the collider physics of the multicharged vectorlike fermions, considering some benchmark points in the allowed parameter space.

hep-ph↗
arXiv2022

Heavy Majorana neutrino pair production from $Z^\prime$ at hadron and lepton colliders

A gauged U$(1)$ extension of the Standard Model (SM) is a simple and anomaly free framework where three generations of Majorana type right-handed neutrinos (RHNs) are introduced to generate light neutrino mass and flavor mixings through the seesaw mechanism. We investigate such models at different hadron and lepton colliders via $Z^\prime$ induced Majorana type RHNs pair production. We derive bounds on U$(1)$ gauge coupling $(g^\prime)$ comparing the model cross sections with experimentally observed data for different $Z^\prime$ mass $(M_{Z^\prime})$ and RHNs mass $(M_N)$. Using these limits we estimate the allowed RHN pair production cross section which can be manifested by lepton number violating signatures in association with fat-jets at the hadron colliders depending on the mass of the RHNs. Hence we study dilepton and trilepton modes with fat-jet/s of the signal for different benchmark values of $M_{Z^\prime}$ and $M_N$. Using fat-jet signatures and studying the signal and corresponding SM backgrounds, we estimate bounds on $M_N-M_{Z^\prime}$ plane at different center of mass energies which could be probed at different hadron colliders. In the context of the lepton colliders we consider electron positron initial states where Majorana type RHNs can be produced from $Z^\prime$ manifesting same sign dilepton plus jets signature and trilepton plus jets in association with missing energy. Studying the signal and corresponding SM backgrounds we estimate the bounds on the $M_N-M_{Z^\prime}$ plane for different center of mass energies. In the context of U$(1)$ extension of the SM there is an SM singlet BSM scalar which couples with the RHNs. We can probe the Majorana nature of RHNs via this BSM scalar production at electron positron colliders.

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