1,659 research outputs found
Exploring the neutrino mass matrix at M_R scale
We discuss the neutrino mass matrix which predicts zero or small values of
|V_{13}| in MSSM and found the inequality, sin^2 2theta_{12} <= sin^2
2theta_sol, where sin^2 2theta_{12} is the mixing angle at M_R scale and sin^2
2theta_{sol} is the value determined by the solar neutrino oscillation. This
constraint says that the model which predicts a larger value of tan^2
theta_{sol} at M_R than the experimental value is excluded. In particular, the
bi-maximal mixing scheme at M_R scale is excluded, from the experimental value
tan^2 theta_sol<1. In this model, |V_{13}| and a Dirac phase at m_Z are induced
radiatively and turn out to be not small. The effective neutrino mass is
expected to be of order 0.05 eV.Comment: revtex4, 20 pages, 6 figure
SO(10) GUT and Quark-Lepton Mass Matrices
The phenomenological model that all quark and lepton mass matrices have the
same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is
discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass
matrices of type I for quarks are consistent with the experimental data in the
quark sector. For the lepton sector, consistent fitting to the data of neutrino
oscillation experiments force us to use the mass matrix for the charged leptons
which is slightly deviated from type I. Given quark masses and charged lepton
masses, the model includes 19 free parameters, whereas the SO(10) GUTs gives 16
constrained equations. Changing the remaining three parameters freely, we can
fit all the entries of the CKM quark mixing matrix and the MNS lepton mixing
matrix, and three neutrino masses consistently with the present experimental
data.Comment: 32pp, REV TeX, 12 EPS Figure
Electric Charge Quantization
Experimentally it has been known for a long time that the electric charges of
the observed particles appear to be quantized. An approach to understanding
electric charge quantization that can be used for gauge theories with explicit
factors -- such as the standard model and its variants -- is
pedagogically reviewed and discussed in this article. This approach uses the
allowed invariances of the Lagrangian and their associated anomaly cancellation
equations. We demonstrate that charge may be de-quantized in the
three-generation standard model with massless neutrinos, because differences in
family-lepton--numbers are anomaly-free. We also review the relevant
experimental limits. Our approach to charge quantization suggests that the
minimal standard model should be extended so that family-lepton--number
differences are explicitly broken. We briefly discuss some candidate extensions
(e.g. the minimal standard model augmented by Majorana right-handed neutrinos).Comment: 18 pages, LaTeX, UM-P-92/5
Unified Explanation of Quark and Lepton Masses and Mixings in the Supersymmetric SO(10) Model
We discussed neutrino masses and mixings in SUSY SO(10) model where quarks
and leptons have Yukawa couplings to at least two 10 and one Higgs
scalars. In this model, the Dirac and the right-handed Majorana mass terms are
expressed by linear combinations of quark and charged lepton mass matrices,
which then determine the neutrino mass matrix by the see-saw mechanism. We show
that there are various solutions to reproduce a large mixing angle for
and a small mixing angle for , as well as the
hierarchical mass spectrum of neutrinos.Comment: LaTeX, 32 pages including 15 eps figure
Search for Millicharged Particles at SLAC
Particles with electric charge q < 10^(-3)e and masses in the range 1--100
MeV/c^2 are not excluded by present experiments. An experiment uniquely suited
to the production and detection of such "millicharged" particles has been
carried out at SLAC. This experiment is sensitive to the infrequent excitation
and ionization of matter expected from the passage of such a particle. Analysis
of the data rules out a region of mass and charge, establishing, for example, a
95%-confidence upper limit on electric charge of 4.1X10^(-5)e for millicharged
particles of mass 1 MeV/c^2 and 5.8X10^(-4)e for mass 100 MeV/c^2.Comment: 4 pages, REVTeX, multicol, 3 figures. Minor typo corrected. Submitted
to Physical Review Letter
Bimaximal mixing from the leptonic new texture for triangular mass matrices
An analysis of the leptonic texture for the new triangular mass matrices has
been carried out. In particular, it is shown that both bimaximal and nearly
bimaximal solutions for solar and atmospheric neutrino anomalies can be
generated within this pattern. We have also derived exact and compact
parametrization of the leptonic mixing matrix in terms of the lepton masses and
the parameters and . A consistency with the CHOOZ
reactor result for and a smallness of the Jarlskog's invariant
parameter are obtained.Comment: 16 pages, late
Measurements of Primary and Atmospheric Cosmic-Ray Spectra with the BESS-TeV Spectrometer
Primary and atmospheric cosmic-ray spectra were precisely measured with the
BESS-TeV spectrometer. The spectrometer was upgraded from BESS-98 to achieve
seven times higher resolution in momentum measurement. We report absolute
fluxes of primary protons and helium nuclei in the energy ranges, 1-540 GeV and
1-250 GeV/n, respectively, and absolute flux of atmospheric muons in the
momentum range 0.6-400 GeV/c.Comment: 26 pages, 9 figures, 3 tables, Submitted to Phys. Lett.
Hierarchical Quark Mass Matrices
I define a set of conditions that the most general hierarchical Yukawa mass
matrices have to satisfy so that the leading rotations in the diagonalization
matrix are a pair of (2,3) and (1,2) rotations. In addition to Fritzsch
structures, examples of such hierarchical structures include also matrices with
(1,3) elements of the same order or even much larger than the (1,2) elements.
Such matrices can be obtained in the framework of a flavor theory. To leading
order, the values of the angle in the (2,3) plane (s_{23}) and the angle in the
(1,2) plane (s_{12}) do not depend on the order in which they are taken when
diagonalizing. We find that any of the Cabbibo-Kobayashi-Maskawa matrix
parametrizations that consists of at least one (1,2) and one (2,3) rotation may
be suitable. In the particular case when the s_{13} diagonalization angles are
sufficiently small compared to the product s_{12}s_{23}, two special CKM
parametrizations emerge: the R_{12}R_{23}R_{12} parametrization follows with
s_{23} taken before the s_{12} rotation, and vice versa for the
R_{23}R_{12}R_{23} parametrization.Comment: LaTeX, 19 pages. References added, minor changes in text. Version
published in Phys. Rev.
R-parity Conserving Supersymmetry, Neutrino Mass and Neutrinoless Double Beta Decay
We consider contributions of R-parity conserving softly broken supersymmetry
(SUSY) to neutrinoless double beta (\znbb) decay via the (B-L)-violating
sneutrino mass term. The latter is a generic ingredient of any weak-scale SUSY
model with a Majorana neutrino mass. The new R-parity conserving SUSY
contributions to \znbb are realized at the level of box diagrams. We derive
the effective Lagrangian describing the SUSY-box mechanism of \znbb-decay and
the corresponding nuclear matrix elements. The 1-loop sneutrino contribution to
the Majorana neutrino mass is also derived.
Given the data on the \znbb-decay half-life of Ge and the neutrino
mass we obtain constraints on the (B-L)-violating sneutrino mass. These
constraints leave room for accelerator searches for certain manifestations of
the 2nd and 3rd generation (B-L)-violating sneutrino mass term, but are most
probably too tight for first generation (B-L)-violating sneutrino masses to be
searched for directly.Comment: LATEX, 29 pages + 4 (uuencoded) figures appende
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