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Teruyuki Kitabayashi

Publications and source records attributed to Teruyuki Kitabayashi.

64 records · Page 4Linked to original sources
arXiv2001

Large Solar Neutrino Mixing in an Extended Zee Model

The Zee model, which employs the standard Higgs scalar ($ϕ$) with its duplicate ($ϕ^\prime$) and a singly charged scalar ($h^+$), can utilize two global symmetries associated with the conservation of the numbers of $ϕ$ and $ϕ^\prime$, $N_{ϕ,ϕ^\prime}$, where $N_ϕ+N_{ϕ^\prime}$ coincides with the hypercharge while $N_ϕ-N_{ϕ^\prime}$ ($\equiv X$) is a new conserved charge, which is identical to $L_e-L_μ-L_τ$ for the left-handed leptons. Charged leptons turn out to have $e$-$μ$ and $e$-$τ$ mixing masses, which are found to be crucial for the large solar neutrino mixing. In an extended version of the Zee model with an extra triplet Higgs scalar (s), neutrino oscillations are described by three steps: 1) the maximal atmospheric mixing is induced by democratic mass terms supplied by $s$ with $X$=2 that can initiate the type II seesaw mechanism for the smallness of these masses; 2) the maximal solar neutrino mixing is triggered by the creation of radiative masses by $h^+$ with $X$ = 0; 3) the large solar neutrino mixing is finally induced by a $ν_μ$-$ν_τ$ mixing arising from the rotation of the radiative mass terms as a result of the diagonalization that converts $e$-$μ$ and $e$-$τ$ mixing masses into the electron mass.

hep-ph↗
arXiv2001

The Interplay between Neutrinos and Charged Leptons in the Minimal SU(3)_LxU(1)_N Gauge Model

In the minimal SU(3)_LxU(1)_N gauge model with a global L_e-L_mu-L_tau (=L') symmetry and a discrete Z_4 symmetry, it is found that the interplay between neutrinos and charged leptons contained in triplets of ψ^i=(ν^i_L, \ell^i_L, \ell^{ci}_L) (i=1,2,3) naturally leads to the large mixing angle (LMA) MSW solution. The model includes two (anti)sextet Higgs scalars, S^(0) with L'=0 and S^(+) with L'=2, which, respectively, couple to ψ^1ψ^{2,3} for the electron mass and masses of atmospheric neutrinos and to ψ^{2,3}ψ^{2,3} for the μ- and τ-masses and one-loop radiative neutrino masses relevant to solar neutrinos. This mechanism is realized by utilizing an additional residual discrete symmetry supplied by explicitly broken L', which guarantees the absence of tree-level neutrino mass terms of the ψ^{2,3}ψ^{2,3}-type. Pure rotation effects due to the diagonalization of neutrino and charged-lepton mass matrices are estimated to yield Δm^2_\odot/Δm^2_{atm} \leq (m_e/m_μ)^{3/2}=O(10^{-4}) but the radiative effects supersede the rotation effects to yield Δm^2_\odot/Δm^2_{atm}=O(10^{-2}) as the LMA solution.

hep-ph↗
arXiv2001

Comment on Neutrino Masses and Oscillations in an $SU(3)_L \times U(1)_N$ Model with Radiative Mechanism

We discussed how neutrino masses and oscillations are radiatively generated in an $SU(3)_L$ $\times$ $U(1)_N$ gauge model with a symmetry based on $L_e-L_μ-L_τ$ ($\equiv$$L^\prime$). The model is characterized by lepton triplets $ψ^i=(ν^i,\ell^{-i},E^{-i})$, where $E^{-i}$ are negatively charged heavy leptons, an $SU(3)_L$ triplet Higgs scalar $ξ$ and a singlet Higgs scalar $k^{++}$. These Higgs scalars can be interpreted as a Zee's and Zee-Babu's scalar for radiative mechanisms. We demonstrated that the mass hierarchy of $Δm_{atm}^2$ $\gg$ $Δm_\odot^2$ arise as a consequence of the dynamical hierarchy between $L^\prime$-conserving one-loop effects and $L^\prime$-violating two-loop effects, and our model is relevant to yield quasivacuum solution for solar neutrino problem.

hep-ph↗
arXiv2001

Large Mixing Angle MSW Solution in an SU(3)_LxU(1)_N Gauge Model with Two-loop Radiative Mechanism

An SU(3)_L x U(1)_N gauge model, where E^{-i} (i=1,2,3) as heavy leptons are placed in the third member of lepton triplets, is shown to provide the large mixing angle (LMA) MSW solution to the solar neutrino problem. By introducing approximate conservation of L_e-L_mu-L_tau (\equiv L') into the model, we have estimated Δm_\odot^2 \sim \sqrt{2}εΔm_{atm}^2m_{E^1}/(m_{E^2}+m_{E^3}), where εrepresents L'-breaking effects and m_{E^i} is a mass of E^{-i}. Since Δm_{atm}^2 \sim 3 x 10^{-3} eV^2, the LMA solution is obtained for ε\sim 0.01-0.1 in the case of m_{E^1} \sim m_{E^{2,3}}. This mechanism utilizes two-loop radiative mechanism, which contains a triplet version of the singly charged Zee boson, h^+, given by ξ= (ξ^{++}, {\bar ξ}^+, h^+)^T. Almost bimaximal mixing is dynamically realized by the approximate equality between the ξ-couplings of the first family to the second and third families.

hep-ph↗
arXiv2001

Two-loop Radiative Neutrino Mechanism in an $SU(3)_L\times U(1)_N$ Gauge Model

By using the $L_e$ - $L_μ$ - $L_τ$ symmetry, we construct an $SU(3)_L\times U(1)_N$ gauge model that provides two-loop radiative neutrino masses as well as one-loop radiative neutrino masses. The generic smallness of two-loop neutrino masses leading to $Δm^2_\odot$ compared with one-loop neutrino masses leading to $Δm^2_{atm}$ successfully explains $Δm^2_{atm}$ $>>$ $Δm^2_{\odot}$ by invoking the $L_e$ - $L_μ$ - $L_τ$ breaking. The Higgs scalar ($h^+$) that initiates radiative mechanisms is unified into a Higgs triplet together with the standard Higgs scalar ($ϕ^+$, $ϕ^0$) to form ($ϕ^+$, $ϕ^0$, $h^+$), which calls for three families of lepton triplets: ($ν^i_L$, $\ell^i_L$, $ω^i_L$) (i = 1,2,3), where $ω^i$ denote heavy neutral leptons. The two-loop radiative mechanism is found possible by introducing a singly charged scalar, which couples to $\ell^i_Rω^j_R$ (i,j = 2,3).

hep-ph↗
arXiv2001

Radiatively Induced Neutrino Masses and Oscillations in an SU(3)_LxU(1)_N Gauge Model

We have constructed an $SU(3)_L \times U(1)_N$ gauge model utilizing an $U(1)_{L^\prime}$ symmetry, where $L^\prime$ = $L_e-L_μ-L_τ$, which accommodates tiny neutrino masses generated by $L^\prime$-conserving one-loop and $L^\prime$-breaking two-loop radiative mechanisms. The generic smallness of two-loop radiative effects compared with one-loop radiative effects describes the observed hierarchy of $Δm_{atm}^2$ $\gg$ $Δm_\odot^2$. A key ingredient for radiative mechanisms is a charged scalar ($h^+$) that couples to charged lepton-neutrino pairs and $h^+$ together with the standard Higgs scalar ($ϕ$) can be unified into a Higgs triplet as ($ϕ^0$, $ϕ^-$, $h^+$)$^T$. This assignment in turn requires lepton triplets ($ψ_L^i$) with heavy charged leptons ($κ_L^{+i}$) as the third member: $ψ_L^i=(ν^i_L,\ell^i_L,κ^{+i}_L)^T$, where $i$ ($=1,2,3$) denotes three families. It is found that our model is relevant to yield quasi-vacuum oscillations for solar neutrinos.

hep-ph↗
arXiv2000

Neutrino Oscillations Induced by Two-loop Radiative Effects

Phenomena of neutrino oscillations are discussed on the basis of two-loop radiative neutrino mechanism. Neutrino mixings are experimentally suggested to be maximal in both atmospheric and solar neutrino oscillations. By using $L_e - L_μ- L_τ$ ($\equiv L^\prime$)-conservation, which, however, only ensures the maximal solar neutrino mixing, we find that two-loop radiative mechanism dynamically generates the maximal atmospheric neutrino mixing and that the estimate of $Δm^2_\odot/Δm^2_{atm} \simεm_e/m_τ$ explains $Δm^2_\odot/Δm^2_{atm} \ll 1$ because of $m_e/m_τ\ll 1$, where $ε$ measures the breaking of the $L^\prime$-conservation. Together with $Δm^2_{atm} \approx 3\times 10^{-3}$ eV$^2$, this estimate yields $Δm^2_\odot \sim 10^{-7}$ eV$^2$ for $ε\sim 0.1$, which corresponds to the LOW solution to the solar neutrino problem. Neutrino mass scale is given by $(16π^2)^{-2} m_em_τ/M$ ($M \sim$ 1 TeV), which is of order 0.01 eV.

hep-ph↗
arXiv2000

Two-loop Radiative Corrections to Neutrino Masses in $SU(3)_L \times U(1)_N$ Gauge Models

We have constructed two $SU(3)_L \times U(1)_N$ gauge models with the $L^\prime = L_e-L_μ-L_τ$ symmetry, which accommodate tiny neutrino masses generated by one-loop and two-loop radiative effects. The heavy neutral leptons and heavy charged leptons are employed to specify the lepton triplets in $SU(3)_L$, respectively, accompanied by ($ϕ^0$, $ϕ^-$, $h^+$) and ($ϕ^+$, $ϕ^0$, $h^+$), where $ϕ$ stands for the standard Higgs scalar and $h^+$ is a key ingredient for radiative mechanisms. From our numerical calculations, we find that both our models are relevant to yield the VO solution to the solar neutrino problem.

hep-ph↗
arXiv2000

Neutrino Oscillations Induced by Two-loop Radiative Mechanism

Two-loop radiative mechanism, when combined with an U(1)_{L'} symmetry generated by L_e-L_μ-L_τ(=L'), is shown to provide an estimate of Δm^2_{\odot}/Δm^2_{atm} $\sim$ εm_e/m_τ, where εmeasures the U(1)_{L'}-breaking. Since Δm^2_{atm} $\sim 3.5x10^{-3} eV^2, we find that Δm^2_{\odot} $\sim$ εx10^{-6} eV^2, which will fall into the allowed region of the LOW solution to the solar neutrino problem for ε$\sim$ 0.1.

hep-ph↗