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J. Sato

Publications and source records attributed to J. Sato.

30 records · Page 2Linked to original sources
arXiv2001

Ambiguities of theoretical parameters and CP/T violation in neutrino factories

We study the optimal setup for observation of the CP asymmetry in neutrino factory experiments --- the baseline length, the muon energy and the analysis method. First, we point out that the statistical quantity which has been used in previous works doesn't represent the CP asymmetry. Then we propose the more suitable quantity, $\equiv χ^{2}_{2} $, which is sensitive to the CP asymmetry. We investigate the behavior of $ χ^{2}_{2} $ with ambiguities of the theoretical parameters. The fake CP asymmetry due to the matter effect increases with the baseline length and hence the error in the estimation of the fake CP asymmetry grows with the baseline length due to the ambiguities of the theoretical parameters. Namely, we lose the sensitivity to the genuine CP-violation effect in longer baseline.

hep-ph↗
arXiv2001

Phenomenology of Neutrino Mass Matrix

The search for possible mixing patterns of charged leptons and neutrinos is important to get clues of the origin of nearly maximal mixings, since there are some preferred bases of the lepton mass matrices given by underlying theories. We systematically examine the mixing patterns which could lead to large lepton mixing angles. We find out 37 mixing patterns are consistent with experimental data if taking into account phase factors in the mixing matrices. Only 6 patterns of them can explain the observed data without any tuning of parameters, while the others need particular choices for phase values.

hep-ph↗
arXiv2000

Matter profile effect in neutrino factory

We point out that the matter profile effect --- the effect of matter density fluctuation on the baseline --- is very important to estimate the parameters in a neutrino factory with a very long baseline. To make it clear, we propose the method of the Fourier series expansion of the matter profile. By using this method, we can take account of both the matter profile effect and its ambiguity. For very long baseline experiment, such as L=7332km, in the analysis of the oscillation phenomena we need to introduce a new parameter $ a_{1} $--- the Fourier coefficient of the matter profile --- as a theoretical parameter to deal with the matter profile effects.

hep-ph↗
arXiv2000

A Constraint on Yukawa-Coupling Unification from Lepton-Flavor Violating Processes

We present a new constraint on a lepton mixing matrix $V$ from lepton-flavor violating (LFV) processes in supersymmetric standard models with massive neutrinos. Here, we assume Yukawa-coupling unification $f_{ν3}\simeq f_{\rm top}$, in which $τ$-neutrino Yukawa coupling $f_{ν3}$ is unified into top-quark Yukawa coupling $f_{\rm top}$ at the unification scale $M_*\simeq 3\times 10^{16}$ GeV. We show that the present experimental bound on $μ\to e γ$ decay already gives a stringent limit on the lepton mixing (typically $V_{13}<0.02$ for $V_{23}=1/\sqrt{2}$). Therefore, many existing neutrino-mass models are strongly constrained. Future improvement of bounds on LFV processes will provide a more significant impact on the models with the Yukawa-coupling unification. We also stress that a precise measurement of a neutrino mixing $(V_{MNS})_{e3}$ in future neutrino experiments would be very important, since the observation of non-zero $(V_{MNS})_{e3}$, together with negative experimental results for the LFV processes, have a robust potential to exclude a large class of SUSY standard models with the Yukawa-coupling unification.

hep-ph↗
arXiv2000

Low-Energy Predictions of Lopsided Family Charges

We consider the Froggatt-Nielsen (FN) mechanism reproducing the observed mass hierarchies and mixing angles for quarks and leptons. The large $ν_μ$-$ ν_τ$ mixing suggested from recent Superkamiokande experiments on the atmospheric neutrinos implies lopsided FN U(1) charges for the lepton doublets. There are two possible charge assignments to generate the large $ν_μ$-$ ν_τ$ mixing. We point out that the two models with different charge assignments have distinct low-energy predictions and hence they are distinguishable in future neutrino experiments on such as CP violation and $2β0ν$ decay.

hep-ph↗
arXiv1999

The Auxiliary Mass Method beyond the Local Potential Approximation

We show that the evolution equation of the effective potential in the auxiliary mass method corresponds to a leading approximation of a certain series. This series is derived from an evolution equation of an effective action using a derivative expansion. We derived an expression of the next-to-leading approximation of the evolution equation, which is a simultaneous partial differential equation.

hep-ph↗
arXiv1999

End-point of the Electroweak Phase Transition using the auxiliary mass method

We study the end-point of the Electroweak phase transition using the auxiliary mass method. The end point is $m_H\sim40$ (GeV) in the case $m_t=0$ (GeV) and strongly depends on the top quark mass. A first order phase transition disappears at $m_t\sim 160$ (GeV). The renormalization effect of the top quark is significant.

hep-ph↗
arXiv1998

Quark and Lepton Mass Matrix in an Asymptotically Non-Free Theory

We analyze fermion mass-matrix structure in an asymptotically non-free model with 4 + 1bar generations. The texture at the GUT scale is uniquely determined by supposing that the masses of heavy up-type quarks (charm as well as top) are realized as their infrared fixed point values. By assuming SO(10) GUT-like relations for Yukawa couplings in this model, this texture can explain all fermion masses and quark mixing with only one small parameter, which is almost equal to the Cabibbo angle.

hep-ph↗
arXiv1998

Large Lepton Mixing in Seesaw Models - Coset-space Family Unification -

We show that the large mixing between $ν_μ$ and $ν_τ$ observed by the SuperKamiokande collaboration is a quite natural prediction in a large class of seesaw models. This large mixing is basically due to the unparallel family structure suggested from the observed mass hierarchies in quark and lepton mass matrices. We show that the unparallel family structure is automatically realized in ``coset-space family unification'' model based on $E_7/SU(5) \times U(1)^3$. This model also suggests the small angle MSW solution to the solar neutrino problem.

hep-ph↗
arXiv1997

Large Lepton Mixing in a Coset-space Family Unification on $E_7/SU(5) \times U(1)^3$

We study a coset-space unification model for families based on $E_7/SU(5) \times U(1)^3$. We find that qualitative structure of quark and lepton mass matrices in this model describes very well the observation. We stress, in particular, that the large mixing angle, $\sin^22θ_{ν_μν_τ} \simeq 1$, required for the atmospheric neutrino oscillation reported by the SuperKamiokande collaboration, is naturally obtained, which is a consequence of unparallel family structure in the present coset-space unification.

hep-ph↗