arXiv subjects

Ichiro Aizawa

Publications and source records attributed to Ichiro Aizawa.

7 recordsLinked to original sources

arXiv2005

A New Type of Complex Neutrino Mass Texture and mu-tau Symmetry

Relying upon the usefulness of the μ-τsymmetry, we find a new type of neutrino mass texture with a single phase parameter δthat describes maximal atmospheric neutrino mixing and Dirac CP violation due to the presence of δ. The Majorana phase associated with the third massive neutrino turns out to be identical to the Dirac phase while other Majorana phases vanish. The nonvanishing reactor neutrino mixing angle θ_{13} is induced by a μ-τsymmetry breaking effect. Flavor neutrino masses that supply the μ-τsymmetry breaking terms become pure imaginary for δ=\pm π/2, leading to maximal CP violation. There is a parameter denoted by η, which is either O(\sqrt{Δm^2_\odot/Δm^2_{atm}}) in the normal mass hierarchy, or O(Δm^2_\odot/Δm^2_{atm}) in the inverted mass hierarchy. In the inverted mass hierarchy, the contribution of O(\sin^2θ_{13}) is found to be significant and cannot be neglected. Our texture also leads to quasi degenerate neutrinos with masses of O(\sqrt{Δm^2_{atm}}), which serves as the scale for the effective neutrino mass in (ββ)_{0ν}-decay. This texture does not include η, and Δm^2_\odot naturally arises from contributions of O(\sin^2θ_{13}) to give Δm^2_\odot/Δm^2_{atm}\sim\sin^2θ_{13}, yielding the prediction of \sin^2θ_{13}=O(10^{-2}).

hep-ph↗

arXiv2005

Determination of Neutrino Mass Texture for Maximal CP Violation

We show a general form of neutrino mass matrix (M), whose matrix elements are denoted by M_{ij} (i.j=e, mu, tau) as flavor neutrino masses, that induces maximal CP violation as well as maximal atmospheric neutrino mixing. The masses of M_{mu mu}, M_{tau tau} and M_{mu tau}+sigma M_{ee} (sigma =\pm 1) turn out to be completely determined by M_{e mu} and M_{e tau} for given mixing angles. The appearance of CP violation is found to originate from the interference between the mu-tau symmetric part of M and its breaking part. If |M_{e mu}|=|M_{e tau}|, giving either M_{e mu}=-sigma e^{i theta} M_{e tau} or M_{e mu}=-sigma e^{i theta}M*_{e tau} with a phase parameter theta, is further imposed, we find that |M_{mu mu}|=|M_{tau tau}|is also satisfied. These two constraints can be regarded as an extended version of the constraints in the mu-tau symmetric texture given by M_{e mu}=-sigma M_{e tau} and M_{mu mu}=M_{tau tau}. Majorana CP violation becomes active if arg(M_{mu tau})\neq arg(M_{e mu})+theta/2 for M_{e mu}=-sigma e^{i theta} M_{e tau} and if arg(M_{mu tau})\neq theta/2 for M_{e mu}=-sigma e^{i theta} M*_{e tau}.

hep-ph↗

arXiv2005

Neutrino Mass Textures with Maximal CP Violation

We have found three types of neutrino mass textures, which give maximal CP-violation as well as maximal atmospheric neutrino mixing. These textures are described by six real mass parameters: one specified by two complex flavor neutrino masses and two constrained ones and the others specified by three complex flavor neutrino masses. In each texture, we calculate mixing angles and masses as well as Majorana CP phases.

hep-ph↗

arXiv2005

Constraints on Flavor Neutrino Masses and sin^2(2theta_{12})>>sin^2(theta_{13}) in Neutrino Oscillations

To realize the condition of sin^2(2theta_{12})>>sin^2(theta_{13}), we find constraints on flavor neutrino masses M_{ij} (ij=e,μ,τ): C1) c_{23}^2 M_{μμ} + s_{23}^2 M_{ττ} \approx 2 s_{23} c_{23}M_{μτ} + M_{ee} and/or C2) |c_{23}M_{eμ} -s_{23}M_{eτ}|>> |s_{23}M_{eμ} +c_{23}M_{eτ}|, where c_{23}=cos(theta_{23}) (s_{23}=sin(theta_{23})) and theta_{12}, theta_{13} and theta_{23} are the mixing angles for three flavor neutrinos. The applicability of C1) and C2) is examined in models with one massless neutrino and two massive neutrinos suggested by \det(M)=0, where M is a mass matrix constructed from M_{ij} (i,j=e,μ,τ). To make definite predictions on neutrino masses and mixings, especially on sin(theta_{13}), that enable us to trace C1) and C2), M is assumed to possess texture zeros or to be constrained by textures with M_{μμ}=M_{ττ} or M_{eτ}=\pm M_{eμ} which turn out to ensure the emergence of the maximal atmospheric neutrino mixing at sin(theta_{13})->0. It is found that C1) is used by textures such as M_{eμ}=0 or M_{eτ}=0 while C2) is used by textures such as M_{eτ}=\pm M_{eμ}.

hep-ph↗

arXiv2004

General Property of Neutrino Mass Matrix and CP Violation

It is found that the atmospheric neutrino mixing angle of θ_{atm} is determined to be \tanθ_{atm}=Im(B)/Im(C) for B=M_{ν_eν_μ} and C=M_{ν_eν_τ}, where M_{ij} is the ij element of M^\dagger_νM_νwith M_νas a complex symmetric neutrino mass matrix in the (ν_e, ν_μ, ν_τ)-basis. Another mixing angle, θ_{13}, defined as U_{e3} = \sinθ_{13}e^{-iδ} is subject to the condition: \tan 2θ_{13} \propto |\sinθ_{atm}B+\cosθ_{atm}C| and the CP-violating Dirac phase of δis identical to the phase of \sinθ_{atm}B^\ast+\cosθ_{atm}C^\ast. The smallest value of |\sin θ_{13}| is achieved at \tanθ_{atm}=-Re(C)/Re(B) that yields the maximal CP-violation and that implies C=-κB^\ast for the maximal atmospheric neutrino mixing of \tanθ_{atm}=κ=\pm 1. The generic smallness of |\sin θ_{13}| can be ascribed to the tiny violation of the electron number conservation.

hep-ph↗

arXiv2004

Bilarge Neutrino Mixing and μ- τPermutation Symmetry for Two-loop Radiative Mechanism

The presence of approximate electron number conservation and μ-τpermutation symmetry of S_2 is shown to naturally provide bilarge neutrino mixing. First, the bimaximal neutrino mixing together with U_{e3}=0 is guaranteed to appear owing to S_2 and, then, the bilarge neutrino mixing together with |U_{e3}|<<1 arises as a result of tiny violation of S_2. The observed mass hierarchy of Δm^2_{\odot}<<Δm^2_{atm} is subject to another tiny violation of the electron number conservation. This scenario is realized in a specific model based on SU(3)_L x U(1)_N with two-loop radiative mechanism for neutrino masses. The radiative effects from heavy leptons contained in lepton triplets generate the bimaximal structure and those from charged leptons, which break S_2, generate the bilarge structure together with |U_{e3}|<<1. To suppress dangerous flavor-changing neutral current interactions due to Higgs exchanges especially for quarks, this S_2 symmetry is extended to a discrete Z_8 symmetry, which also ensures the absence of one-loop radiative mechanism.

hep-ph↗

arXiv2003

Dilatonic Inflation and SUSY Breaking in String-inspired Supergravity

The theory of inflation will be investigated as well as supersymmetry breaking in the context of supergravity, incorporating the target-space duality and the nonperturbative gaugino condensation in the hidden sector. We found an inflationary trajectory of a dilaton field and a condensate field which breaks supersymmetry at once. The model satisfies the slow-roll condition which solves the eta-problem. When the particle rolls down along the minimized trajectory of the potential V(S,Y) at a duality invariant point of T=1, we can obtain the e-fold value \sim 57. And then the cosmological parameters obtained from our model well match the recent WMAP data combined with other experiments. This observation suggests one to consider the string-inspired supergravity as a fundamental theory of the evolution of the universe as well as the particle theory.

hep-ph↗