55 research outputs found
Lepton mixing angle with a horizontal symmetry
We discuss a model for the lepton sector based on the seesaw mechanism and on
a family symmetry. The model predicts the mixing angle to
vanish. The solar mixing angle is free--it will in general be
large if one does not invoke finetuning. The model has an enlarged scalar
sector with three Higgs doublets, together with two real scalar gauge singlets
() which have vacuum expectation values _0\theta_{23}\tan
\theta_{23} = _0, and it is maximal if the Lagrangian is
-invariant; but may be broken softly, by a term of dimension two in
the scalar potential, and then < \chi_2_0 becomes different from < \chi_1_0.
Thus, the strength of the soft breaking controls the deviation of
from . The model predicts a normal neutrino mass
spectrum () and allows successful leptogenesis if ; these properties of the model are independent of
the presence and strength of the soft breaking.Comment: 13 pages, one figur
SO(3) Gauge Symmetry and Neutrino-Lepton Flavor Physics
Based on the SO(3) gauge symmetry for three family leptons and general
see-saw mechanism, we present a simple scheme that allows three nearly
degenerate Majorana neutrino masses needed for hot dark matter. The vacuum
structure of the spontaneous SO(3) symmetry breaking can automatically lead to
a maximal CP-violating phase. Thus the current neutrino data on both the
atmospheric neutrino anomaly and solar neutrino deficit can be accounted for
via maximal mixings without conflict with the current data on the neutrinoless
double beta decay. The model also allows rich interesting phenomena on lepton
flavor violations.Comment: 10 pages, Revtex, no figures, minor changes and references added, the
version to appear in Phys. Rev.
Long Baseline Neutrino Physics with a Muon Storage Ring Neutrino Source
We examine the physics capabilities of known flavor neutrino beams from
intense muon sources. We find that long-baseline neutrino experiments based on
such beams can provide precise measurements of neutrino oscillation mass and
mixing parameters. Furthermore, they can test whether the dominant atmospheric
neutrino oscillations are \nu_\mu --> \nu_\tau and/or \nu_\mu --> \nu_s,
determine the \nu_\mu --> \nu_e content of atmospheric neutrino oscillations,
and measure \nu_e --> \nu_\tau appearance. Depending on the oscillation
parameters, they may be able to detect Earth matter and CP violation effects
and to determine the ordering of some of the mass eigenstates.Comment: 38 pages, Revtex with epsf.sty, 21 postscript figures. Minor text
revisions, some new numbers in Tables II and II
Mu-tau antisymmetry and neutrino mass matrices
Using the seesaw mechanism and a discrete symmetry, we construct a class of
models for the neutrino mass matrix where the inverse of that matrix is the sum
of a mu-tau antisymmetric background and a perturbation. We consider various
possibilities for that perturbation. The simplest possible perturbations lead
to four-parameter neutrino mass matrices which are unable to fit the
experimental data. More complicated perturbations give rise to viable
six-parameter mass matrices; we present detailed predictions of each of them.Comment: 15 pages of text, 7 figure
Probing the seesaw mechanism with neutrino data and leptogenesis
In the framework of the seesaw mechanism with three heavy right-handed
Majorana neutrinos and no Higgs triplets we carry out a systematic study of the
structure of the right-handed neutrino sector. Using the current low-energy
neutrino data as an input and assuming hierarchical Dirac-type neutrino masses
, we calculate the masses and the mixing of the heavy neutrinos.
We confront the inferred properties of these neutrinos with the constraints
coming from the requirement of a successful baryogenesis via leptogenesis. In
the generic case the masses of the right-handed neutrinos are highly
hierarchical: ; the lightest mass is GeV and the generated baryon-to-photon ratio is
much smaller than the observed value. We find the special cases which
correspond to the level crossing points, with maximal mixing between two
quasi-degenerate right-handed neutrinos. Two level crossing conditions are
obtained: (1-2 crossing) and (2-3
crossing), where and are respectively the 11-entry and the
12-subdeterminant of the light neutrino mass matrix in the basis where the
neutrino Yukawa couplings are diagonal. We show that sufficient lepton
asymmetry can be produced only in the 1-2 crossing where GeV, GeV and .Comment: 30 pages, 2 eps figures, JHEP3.cls, typos corrected, note (and
references) added on non-thermal leptogenesi
Probing doubly excited ionic states of N2+ via a triple excitation above the N 1s threshold in the N2 molecule
Angle-resolved resonant Auger-electron spectroscopy has been carried out on the nitrogen molecule at selected photon energies around 419 eV, where a 1s core electron and two valence electrons are promoted into the lowest unoccupied molecular orbital 1πg. Significant enhancement of a specific band, which cannot be disentangled in direct photoionization, is observed at a binding energy of 37.6 eV, with a value of the anisotropy parameter β much smaller than 2. We assign this new band to the transition to a doubly excited cationic state of N2, in which two of the excited valence electrons remain in the 1πg orbital, proposing a "double spectator" type decay mechanism. This observation shows how to preferentially probe multiply excited configurations of cations using multiple resonant excitation
Model for Particle Masses, Flavor Mixing, and CP Violation Based on Spontaneously Broken Discrete Chiral Symmetry as the Origin of Families
We construct extensions of the standard model based on the hypothesis that
the Higgs bosons also exhibit a family structure, and that the flavor weak
eigenstates in the three families are distinguished by a discrete chiral
symmetry that is spontaneously broken by the Higgs sector. We study in detail
at the tree level models with three Higgs doublets, and with six Higgs doublets
comprising two weakly coupled sets of three. In a leading approximation of
cyclic permutation symmetry the three Higgs model gives a ``democratic''
mass matrix of rank one, while the six Higgs model gives either a rank one mass
matrix, or in the case when it spontaneously violates CP, a rank two mass
matrix corresponding to nonzero second family masses. In both models, the CKM
matrix is exactly unity in leading approximation. Allowing small explicit
violations of cyclic permutation symmetry generates small first family masses
in the six Higgs model, and first and second family masses in the three Higgs
model, and gives a non-trivial CKM matrix in which the mixings of the first and
second family quarks are naturally larger than mixings involving the third
family. Complete numerical fits are given for both models, flavor changing
neutral current constraints are discussed in detail, and the issues of
unification of couplings and neutrino masses are addressed. On a technical
level, our analysis uses the theory of circulant and retrocirculant matrices,
the relevant parts of which are reviewed.Comment: Revtex, 59 pages including four tables at en
Bilarge Neutrino Mixing and \mu - \tau Permutation Symmetry for Two-loop Radiative Mechanism
The presence of approximate electron number conservation and \mu-\tau
permutation 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 \Delta m^2_{\odot}<<\Delta m^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.Comment: 18 pages, 7 figures, to appear in Phys. Rev.
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