2,698 research outputs found
Broken S_3 Flavor Symmetry of Leptons and Quarks: Mass Spectra and Flavor Mixing Patterns
We apply the discrete S_3 flavor symmetry to both lepton and quark sectors of
the standard model extended by introducing one Higgs triplet and realizing the
type-II seesaw mechanism for finite neutrino masses. The resultant mass
matrices of charged leptons (M_l), neutrinos (M_nu), up-type quarks (M_u) and
down-type quarks (M_d) have a universal form consisting of two terms: one is
proportional to the identity matrix I and the other is proportional to the
democracy matrix D. We argue that the textures of M_l, M_u and M_d are
dominated by the D term, while that of M_nu is dominated by the I term. This
hypothesis implies a near mass degeneracy of three neutrinos and can naturally
explain why the mass matrices of charged fermions are strongly hierarchical,
why the quark mixing matrix is close to I and why the lepton mixing matrix
contains two large angles. We discuss a rather simple perturbation ansatz to
break the S_3 symmetry and obtain more realistic mass spectra of leptons and
quarks as well as their flavor mixing patterns. We stress that the I term,
which used to be ignored from M_l, M_u and M_d, is actually important because
it can significantly modify the smallest lepton flavor mixing angle theta_13 or
three quark flavor mixing angles.Comment: 13 pages, no figures; discussions about CP violation added,
references updated, to appear in Phys. Lett.
The Glashow resonance as a discriminator of UHE cosmic neutrinos originating from p-gamma and p-p collisions
We re-examine the interesting possibility of utilizing the Glashow resonance
(GR) channel nu_ebar + e^- to W^- to anything to discriminate between the UHE
cosmic neutrinos originating from p-gamma and pp collisions in an optically
thin source of cosmic rays. We propose a general parametrization of the initial
neutrino flavor composition by allowing the ratios Phi^{p gamma}_{pi^-}/Phi^{p
gamma}_{pi^+} and Phi^{pp}_{pi^-}/Phi^{pp}_{pi^+} to slightly deviate from
their conventional values. A relationship between the typical source parameter
kappa = (Phi^{p gamma}_{pi^+} + Phi^{p gamma}_{pi^-})/(Phi^{pp}_{pi^+} +
Phi^{pp}_{pi^-} + Phi^{p gamma}_{pi^+} + Phi^{p gamma}_{pi^-}) and the working
observable of the GR R_0 = Phi^T_{nu_ebar}/ (Phi^T_{nu_mu} + Phi^T_{nu_mu}) at
a neutrino telescope is derived, and the numerical dependence of R_0 on kappa
is illustrated by taking account of the latest experimental data on three
neutrino mixing angles. It is shown that a measurement of R_0 is in principle
possible to identify the pure p-gamma interaction (kappa =1), the pure pp
interaction (kappa =0) or a mixture of both of them (0 < kappa < 1) at a given
source of UHE cosmic neutrinos. The event rate of the GR signal against the
background is also estimated.Comment: 13 pages, 6 figures, final version to appear in Phys. Rev.
Generalized Friedberg-Lee model for neutrino masses and leptonic CP violation from mu-tau symmetry breaking
Assuming the Majorana nature of massive neutrinos, we generalize the
Friedberg-Lee neutrino mass model to include CP violation in the neutrino mass
matrix M_\nu. The most general case with all the free parameters of M_\nu being
complex is discussed. We show that a favorable neutrino mixing pattern (with
\theta_12 \approx 35.3^\circ, \theta_23=45^\circ, \theta_13 \neq 0^\circ and
\delta=90^\circ) can naturally be derived from M_\nu, if it has an approximate
or softly-broken \mu-\tau symmetry. We also point out a different way to obtain
the nearly tri-bimaximal neutrino mixing pattern with \delta=0^\circ and
non-vanishing Majorana phases.Comment: 4 pages. Talk given by He Zhang at the 4th International Conference
on Flavor Physics, 24-28 September 2007, Beijing (to appear in the
proceedings
How to interpret a discovery or null result of the decay
The Majorana nature of massive neutrinos will be crucially probed in the
next-generation experiments of the neutrinoless double-beta ()
decay. The effective mass term of this process, , may
be contaminated by new physics. So how to interpret a discovery or null result
of the decay in the foreseeable future is highly nontrivial. In
this paper we introduce a novel three-dimensional description of , which allows us to see its sensitivity to the lightest
neutrino mass and two Majorana phases in a transparent way. We take a look at
to what extent the free parameters of can be well
constrained provided a signal of the decay is observed someday.
To fully explore lepton number violation, all the six effective Majorana mass
terms (for )
are calculated and their lower bounds are illustrated with the two-dimensional
contour figures. The effect of possible new physics on the decay
is also discussed in a model-independent way. We find that the result of
in the normal (or inverted) neutrino mass ordering
case modified by the new physics effect may somewhat mimic that in the inverted
(or normal) mass ordering case in the standard three-flavor scheme. Hence a
proper interpretation of a discovery or null result of the decay
may demand extra information from some other measurements.Comment: 13 pages, 6 figures, Figures and references update
- …