1,941 research outputs found
Neutrino Masses, Lepton Flavor Mixing and Leptogenesis in the Minimal Seesaw Model
We present a review of neutrino phenomenology in the minimal seesaw model
(MSM), an economical and intriguing extension of the Standard Model with only
two heavy right-handed Majorana neutrinos. Given current neutrino oscillation
data, the MSM can predict the neutrino mass spectrum and constrain the
effective masses of the tritium beta decay and the neutrinoless double-beta
decay. We outline five distinct schemes to parameterize the neutrino
Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis
via leptogenesis are investigated in some detail by taking account of possible
texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on
the CP-violating asymmetry in the decay of the lighter right-handed Majorana
neutrino. The effects of the renormalization-group evolution on the neutrino
mixing parameters are analyzed, and the correlation between the CP-violating
phenomena at low and high energies is highlighted. We show that the observed
matter-antimatter asymmetry of the Universe can naturally be interpreted
through the resonant leptogenesis mechanism at the TeV scale. The
lepton-flavor-violating rare decays, such as , are also
discussed in the supersymmetric extension of the MSM.Comment: 50 pages, 22 EPS figures, macro file ws-ijmpe.cls included, accepted
for publication in Int. J. Mod. Phys.
Exploring the parameter space of texture 4 zero quark mass matrices
We have attempted to extend the parameter space of the elements of the
texture 4 zero Hermitian quark mass matrices, to include the case of `weak
hierarchy' amongst them along with the usually considered `strong hierarchy'
case. This has been carried out by giving wide variation to the hierarchy
defining parameters D_U and D_D, having implications for the structural
features of the mass matrices. We find that not only the weakly hierarchical
mass matrices are able to reproduce the strongly hierarchical mixing angles but
also both the phases having their origin in the mass matrices have to be non
zero to achieve compatibility of these matrices with recent quark mixing data.
Further noting the difference between the exclusive and inclusive values of
V_ub, we have carried out separate analyses corresponding to these.Comment: 13 pages, 4 figures, version accepted for publication in Journal Of
Physics
Flavor Mixing and CP Violation of Massive Neutrinos
We present an overview of recent progress in the phenomenological study of
neutrino masses, lepton flavor mixing and CP violation. We concentrate on the
model-independent properties of massive neutrinos, both in vacuum and in
matter. Current experimental constraints on the neutrino mass spectrum and the
lepton flavor mixing parameters are summarized. The Dirac- and Majorana-like
phases of CP violation, which are associated respectively with the
long-baseline neutrino oscillations and the neutrinoless double beta decay, are
discussed in detail. The seesaw mechanism, the leptogenesis scenario and the
strategies to construct lepton mass matrices are briefly described. The
features of flavor mixing between one sterile neutrino and three active
neutrinos are also explored.Comment: Invited review. LaTex 76 pages (14 PS figures included
Two-zero Textures of the Majorana Neutrino Mass Matrix and Current Experimental Tests
In view of the latest T2K and MINOS neutrino oscillation data which hint at a
relatively large theta_13, we perform a systematic study of the Majorana
neutrino mass matrix M_nu with two independent texture zeros. We show that
three neutrino masses (m_1, m_2, m_3) and three CP-violating phases (delta,
rho, sigma) can fully be determined from two neutrino mass-squared differences
(delta m^2, Delta m^2) and three flavor mixing angles (theta_12, theta_23,
theta_13). We find that seven patterns of M_nu (i.e., A_{1,2}, B_{1,2,3,4} and
C) are compatible with current experimental data at the 3-sigma level, but the
parameter space of each pattern is more strictly constrained than before. We
demonstrate that the texture zeros of M_nu are stable against the one-loop
quantum corrections, and there exists a permutation symmetry between Patterns
A_1 and A_2, B_1 and B_2 or B_3 and B_4. Phenomenological implications of M_nu
on the neutrinoless double-beta decay and leptonic CP violation are discussed,
and a realization of those texture zeros by means of the Z_n flavor symmetries
is illustrated.Comment: 41 pages, including 4 tables and 14 figures, more discussions added,
to appear in JHE
Prediction of in Neutrino Mass Matrix with Two Zeros
We have discussed predictions of and in the framework of
the neutrino mass matrix with two zeros. In the case of the best fit values of
, , and , the prediction of is . The lower
bound of is 0.05, which depends on and
. We have investigated the stability of these predictions
taking account of small corrections to zeros, which may come from radiative
corrections or off-diagonal elements of the charged lepton massmatrix.
The lower bound of comes down considerably due to the small
corrections to zeros.Comment: Figures and discussions are adde
New measurement of via neutron capture on hydrogen at Daya Bay
This article reports an improved independent measurement of neutrino mixing
angle at the Daya Bay Reactor Neutrino Experiment. Electron
antineutrinos were identified by inverse -decays with the emitted
neutron captured by hydrogen, yielding a data-set with principally distinct
uncertainties from that with neutrons captured by gadolinium. With the final
two of eight antineutrino detectors installed, this study used 621 days of data
including the previously reported 217-day data set with six detectors. The
dominant statistical uncertainty was reduced by 49%. Intensive studies of the
cosmogenic muon-induced Li and fast neutron backgrounds and the
neutron-capture energy selection efficiency, resulted in a reduction of the
systematic uncertainty by 26%. The deficit in the detected number of
antineutrinos at the far detectors relative to the expected number based on the
near detectors yielded in the
three-neutrino-oscillation framework. The combination of this result with the
gadolinium-capture result is also reported.Comment: 26 pages, 23 figure
Improved Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay
A new measurement of the reactor antineutrino flux and energy spectrum by the
Daya Bay reactor neutrino experiment is reported. The antineutrinos were
generated by six 2.9~GW nuclear reactors and detected by eight
antineutrino detectors deployed in two near (560~m and 600~m flux-weighted
baselines) and one far (1640~m flux-weighted baseline) underground experimental
halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD)
candidates were detected. The IBD yield in the eight detectors was measured,
and the ratio of measured to predicted flux was found to be
() for the Huber+Mueller (ILL+Vogel) model. A 2.9~
deviation was found in the measured IBD positron energy spectrum compared to
the predictions. In particular, an excess of events in the region of 4-6~MeV
was found in the measured spectrum, with a local significance of 4.4~.
A reactor antineutrino spectrum weighted by the IBD cross section is extracted
for model-independent predictions.Comment: version published in Chinese Physics
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