arXiv subjects

Takaaki Nomura

Publications and source records attributed to Takaaki Nomura.

At least 127 records · Page 7Linked to original sources

arXiv2018

$ε'/ε$ from charged-Higgs-induced gluonic dipole operators

We study the effect of charged-Higgs-induced chromomagnetic operator, $Q_{8G}(-) \equiv \bar s σ^{μν} T^a γ_5 d G^a_{μν}$, on the Kaon direct CP violation $Re(ε'/ε)$. Using the matrix element $\langle ππ| O_{8G}(-) | K^0 \rangle$ recently obtained by a large $N_c$ dual QCD approach, we find that if the Kobayashi-Maskawa phase is the origin of CP violation, the charged-Higgs-induced gluon penguin dipole operator in the type-III two-Higgs-doublet model can explain the measured $Re(ε'/ε)$ when the constraints from the relevant low energy flavor physics, such as $ΔB(K)=2$, $B\to X_s γ$, and Kaon indirect CP violation parameter $ε$, are included.

hep-ph↗

arXiv2018

Charged Higgs boson contribution to $B^-_{q} \to \ell \bar ν$ and $\bar B\to (P, V) \ell \barν$ in a generic two-Higgs doublet model

We comprehensively study the charged-Higgs contributions to the leptonic $B^-_q \to \ell \bar ν$ ($q=u,c$) and semileptonic $\bar B \to X_q \ell \barν$ ($X_u=π, ρ; X_c=D,D^*$) decays in the type-III two-Higgs-doublet model (2HDM). We employ the Cheng-Sher ansatz to suppress the tree-level flavor-changing neutral currents (FCNCs) in the quark sector. When the strict constraints from the $ΔB=2$ and $b\to s γ$ processes are considered, parameters $χ^u_{tq}$ from the quark couplings and $χ^\ell_\ell$ from the lepton couplings dictate the leptonic and semileptonic $B$ decays. It is found that when the measured $B^-_u\to τ\bar ν$ and indirect bound of $B^-_c \to τ\bar ν$ obtained by LEP1 data are taken into account, $R(D)$ and $R(π)$ can have broadly allowed ranges; however, the values of $R(ρ)$ and $R(D^*)$ are limited to approximately the standard model (SM) results. We also find that the same behaviors also occur in the $τ$-lepton polarizations and forward-backward asymmetries ($A^{X_q,τ}_{FB}$) of the semileptonic decays, with the exception of $A^{D^*,τ}_{FB}$, for which the deviation from the SM due to the charged-Higgs effect is still sizable. In addition, the $q^2$-dependent $A^{π,τ}_{FB}$ and $A^{D,τ}_{FB}$ can be very sensitive to the charged-Higgs effects and have completely different shapes from the SM.

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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

$ε_K$ and $ε'/ε$ in a diquark model

Based on the calculations using the lattice QCD by RBC-UKQCD collaboration and a large $N_c$ dual QCD, the resulted $ε'/ε$, which is less than the experimental data by more than a $2σ$ in the standard model (SM), suggests the necessity of a new physics effect. In order to complement the insufficient $ε'/ε$, we study the extension of the SM with a colored scalar in a diquark model. In addition to the pure diquark box diagrams, it is found that the box diagrams with one $W$-boson and one diquark, ignored in the literature, play an important role in the $ΔS=2$ process. The mass difference between $K_L$ and $K_S$ in the diquark model is well below the current data, whereas the Kaon indirect CP violation $ε_K$ gives a strict constraint on the new parameters. Three mechanisms are classified in the study of $ε'/ε$, and they include: tree-level diagram, QCD and electroweak penguins, and chromomagnetic dipole. Taking the Kobayashi-Maskawa phase as the unique CP source, we analyze each contribution of the three mechanisms in detail and conclude that these diquark-mediated effects can singly enhance $ε'/ε$ to be of ${\cal O}(10^{-3})$, depending on the values of free parameters, when the bound from $ε_K$ is satisfied.

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arXiv2018

$ε'_K/ε_K$ and $K \to πν\barν$ in a two-Higgs doublet model

The Kaon direct CP violation $Re(ε'_K/ε_K)$ below the experimental data of a $2σ$ in the standard model, which is calculated using the RBC-UKQCD lattice and a large $N_c$ dual QCD, indicates the necessity of a new physics effect. In order to resolve the insufficient $Re(ε'_K/ε_K)$, we study the charged-Higgs contributions in a generic two-Higgs-doublet model. If we assume that the origin of the CP-violation phase is uniquely from the Kobayashi-Maskawa (KM) phase when the constraints from the $B$- and $K$-meson mixings, $B\to X_s γ$, and Kaon indirect CP violating parameter $ε_K$ are simultaneously taken into account, it is found that the Kaon direct CP violation through the charged-Higgs effects can reach $Re(ε'_K/ε_K)_{H^\pm}\sim 8 \times 10^{-4}$. Moreover, with the constrained values of the parameters, the branching ratios of the rare $K\to πν\barν$ decays can be $BR(K^+\to π^+ ν\barν)\sim 14 \times 10^{-11}$ and $BR(K_L\to π^0 ν\barν)\sim 3.6 \times 10^{-11}$, where the results can be tested through the NA62 experiment at CERN and the KOTO experiment at J-PARC, respectively.

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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.

hep-ph↗

arXiv2018

Scalar dark matter search from the extended $ν$THDM

We consider a neutrino Two Higgs Doublet Model ($ν$THDM) in which neutrinos obtain {\it naturally} small Dirac masses from the soft symmetry breaking of a global $U(1)_X$ symmetry. We extended the model so the soft term is generated by the spontaneous breaking of $U(1)_X$ by a new scalar field. The symmetry breaking pattern can also stabilize a scalar dark matter candidate. After constructing the model, we study the phenomenology of the dark matter: relic density, direct and indirect detection.

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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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arXiv2018

Radiatively Induced Neutrino Mass Model with Flavor Dependent Gauge Symmetry

We study a radiative seesaw model at one-loop level with a flavor dependent gauge symmetry $U(1)_{μ-τ}$, in which we consider bosonic dark matter. We also analyze the constraints from lepton flavor violations, muon $g-2$, relic density of dark matter, and collider physics, and carry out numerical analysis to search for allowed parameter region which satisfy all the constraints and to investigate some predictions. Furthermore we find that a simple but adhoc hypothesis induces specific two zero texture with inverse mass matrix, which provides us several predictions such as a specific pattern of Dirac CP phase.

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arXiv2018

Explaining the DAMPE $e^+ e^-$ excess using the Higgs triplet model with a vector dark matter

We explain the $e^+ e^-$ excess observed by the DAMPE Collaboration using a dark matter model based upon the Higgs triplet model and an additional hidden $SU(2)_X$ gauge symmetry. Two of the $SU(2)_X$ gauge bosons are stable due to a residual discrete symmetry and serve as the dark matter candidate. We search the parameter space for regions that can explain the observed relic abundance, and compute the flux of $e^+ e^-$ coming from a nearby dark matter subhalo. With the inclusion of background cosmic rays, we show that the model can render a good fit to the entire energy spectrum covering the AMS-02, Fermi-LAT and DAMPE data.

hep-ph↗

arXiv2018

Neutrino mass in flavor dependent gauged lepton model

We study a neutrino model introducing an additional nontrivial gauged lepton symmetry where the neutrino masses are induced at two-loop level while the first and second charged-leptons of the standard model are done at one-loop level. As a result of model structure, we can predict one massless active neutrino, and there is a dark matter candidate. Then we discuss neutrino mass matrix, muon anomalous magnetic moment, lepton flavor violations, oblique parameters, and relic density of dark matter taking into account the experimental constraints.

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arXiv2018

Neutrinophilic two Higgs doublet model with dark matter under an alternative $U(1)_{B-L}$ gauge symmetry

We propose Dirac type active neutrino with rank two mass matrix and a Majorana fermion dark matter candidate with an alternative local $U(1)_{B-L}$ extension of neutrinophilic two Higgs doublet model. Our dark matter candidate can be stabilized due to charge assignment under the gauge symmetry without imposing extra discrete $Z_2$ symmetry and the relic density is obtained from $Z'$ boson exchanging process. Taking into account collider constraints on $Z'$ boson mass and coupling, we estimate the relic density.

hep-ph↗

arXiv2018

Discriminating leptonic Yukawa interactions with doubly charged scalar at the ILC

We explore discrimination of two types of leptonic Yukawa interactions associated with Higgs triplet, $\bar L^c_L ΔL_L$, and with $SU(2)$ singlet doubly charged scalar, $\bar e_R^c k^{++} e_R$. These interactions can be distinguished by measuring the effects of doubly charged scalar boson exchange in the $e^+ e^- \to \ell^+ ell^-$ processes at polarized electron-positron colliders. We study a forward-backward asymmetry of scattering angular distribution to estimate the sensitivity for these effects at the ILC. In addition, we investigate prospects of upper bounds on the Yukawa couplings by combining the constraints of lepton flavor violation processes and the $e^+ e^- \to \ell^+ \ell^-$ processes at the LEP and the ILC.

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