150 research outputs found
A bound on neutrino masses from baryogenesis
Properties of neutrinos, the lightest of all elementary particles, may be the
origin of the entire matter-antimatter asymmetry of the universe. This requires
that neutrinos are Majorana particles, which are equal to their antiparticles,
and that their masses are sufficiently small. Leptogenesis, the theory
explaining the cosmic matter-antimatter asymmetry, predicts that all neutrino
masses are smaller than 0.2 eV, which will be tested by forthcoming laboratory
experiments and by cosmology.Comment: 8 pages, 2 figure
Future Precision Neutrino Oscillation Experiments and Theoretical Implications
Future neutrino oscillation experiments will lead to precision measurements
of neutrino mass splittings and mixings. The flavour structure of the lepton
sector will therefore at some point become better known than that of the quark
sector. This article discusses the potential of future oscillation experiments
on the basis of detailed simulations with an emphasis on experiments which can
be done in about ten years. In addition, some theoretical implications for
neutrino mass models will be briefly discussed.Comment: Talk given at Nobel Symposium 2004: Neutrino Physics, Haga Slott,
Enkoping, Sweden, 19-24 Aug 200
Baryogenesis via Lepton Number Violation and Family Replicated Gauge Group
We developed a previous model fitting all quark and lepton -- including
neutrino quantities in the region of the Large Mixing Angle-MSW solar solution
-- order of magnitudewise by only six adjustable parameters (Higgs vacuum
expectation values) to also give an agreeing prediction for the amount of
baryogenesis produced in the early time of cosmology. We use Fukugita-Yanagida
scheme and take into account now also the effect of the remormalisation
equation for the Dirac neutrino sector from Planck scale to the see-saw scale.
The present version of our model with many approximately conserved (gauge)
charges distinguishing various left- and right-Weyl particles has the largest
matrix element of the mass matrix for the three flavour see-saw neutrinos being
the off-diagonal elements associated with the second- and third-proto-flavour
and gives the ratio of baryon number density to the entropy density to
2.59{+17.0\atop-2.25}\times 10^{-11} which agrees perfectly well as do also all
the fermion masses and their mixing angles order of magnitudewise.Comment: 36 pages, 2 feynmf figures, Latex2e; one ref. added, refree responce
slightly modifie
\tau\to \mu \bar{\nu_i} \nu_i decay in the general two Higgs doublet model
We study \tau\to \mu \bar{\nu_i} \nu_i, i=e,\mu,\tau decay in the model III
version of the two Higgs doublet model. We calculated the BR at the order of
the magnitude of 10^{-6}-10^{-4} for the intermediate values of the Yukawa
couplings. Furthermore, we predict the upper limit of the coupling for the
\tau-h^0 (A^0)-\tau transition as \sim 0.3 in the case that the BR is \sim
10^{-6}. We observe that the experimental result of the process under
consideration can give comprehensive information about the physics beyond the
standard model and the free parameters existing.Comment: 9 pages, 5 figure
Pseudo-Dirac Scenario for Neutrino Oscillations
We argue how pseudo-Dirac scenario for neutrinos leads to rich neutrino
oscillation phenomena, including oscillation inside each generation. The
pseudo-Dirac scenario is generalized by incorporating generation mixings and
formulae for the various neutrino oscillations are derived. As the application
we compare the formulae with the corresponding data. We find that observed
pattern of mixings, such as almost maximal mixing in the atmospheric neutrino
oscillation, is naturally explained in the generalized Pseudo-Dirac scenario
with small generation mixings. We, however, also point out that there remain
some problems to be settled for this scenario to be viable. The possible
theoretical framework to realize the pseudo-Dirac scenario is also briefly
commented on.Comment: 17 pages, LaTeX fil
Indications of Neutrino Oscillation in a 250 km Long-baseline Experiment
The K2K experiment observes indications of neutrino oscillation: a reduction
of flux together with a distortion of the energy spectrum. Fifty-six
beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the
neutrino production point, with an expectation of .
Twenty-nine one ring -like events are used to reconstruct the neutrino
energy spectrum, which is better matched to the expected spectrum with neutrino
oscillation than without. The probability that the observed flux at SK is
explained by statistical fluctuation without neutrino oscillation is less than
1%.Comment: 5 pages, 3 figures embedded, LaTeX with RevTeX style, accepted for
publication in PRL on December 13, 200
Measurements of total and partial charge-changing cross sections for 200-400 MeV/nucleon 12C in water and polycarbonate
We have studied charged nuclear fragments produced by 200 - 400 MeV/nucleon carbon ions, interacting with water and polycarbonate, using a newly developed emulsion detector. Total and partial charge-changing cross sections for the production of B, Be, and Li fragments were measured and compared with both previously published measurements, and model predictions. This study is of importance for validating and improving carbon ion therapy treatment planning systems, and for estimating the radiological risks for personnel on space missions, since carbon is a significant component of the Galactic Cosmic Rays
Search for nucleon decay via modes favored by supersymmetric grand unification models in Super-Kamiokande-I
We report the results for nucleon decay searches via modes favored by
supersymmetric grand unified models in Super-Kamiokande. Using 1489 days of
full Super-Kamiokande-I data, we searched for , , and modes. We found no
evidence for nucleon decay in any of these modes. We set lower limits of
partial nucleon lifetime 2.3, 1.3,
1.3 and 1.0 years at 90% confidence level for , , and modes, respectively. These results give a strong constraint on
supersymmetric grand unification models.Comment: 14 pages, 13 figure
Evidence for an oscillatory signature in atmospheric neutrino oscillation
Muon neutrino disappearance probability as a function of neutrino flight
length L over neutrino energy E was studied. A dip in the L/E distribution was
observed in the data, as predicted from the sinusoidal flavor transition
probability of neutrino oscillation. The observed L/E distribution constrained
nu_mu nu_tau neutrino oscillation parameters; 1.9x10^-3 < Delta m^2 <
3.0x10^-3 eV^2 and \sin^2(2theta) > 0.90 at 90% confidence level.Comment: 5 pages, 5 figures, submitted to PR
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