100 research outputs found
Constraints on long-baseline neutrino oscillations from the results of neutrino oscillation experiments
It is shown that in the two schemes with four massive neutrinos which are
compatible with the results of all neutrino oscillation experiments, the
probabilities of nu_e disappearance and nu_mu->nu_e appearance in long-baseline
experiments are severely constrained.Comment: 7 pages, including 2 figures. Talk presented by C. Giunti at TAUP97,
September 7-11, 1997, Laboratori Nazionali del Gran Sasso, Ital
Constraints from Neutrino Oscillation Experiments on the Effective Majorana Mass in Neutrinoless Double -Decay
We determine the possible values of the effective Majorana neutrino mass in the different phenomenologically viable three
and four-neutrino scenarios. The quantities () denote the elements of the neutrino mixing matrix and the
Majorana neutrino masses () are ordered as Assuming in the three-neutrino case and in the
four-neutrino case, we discuss, in particular, how constraints on
depend on the mixing angle relevant in solar neutrino oscillations and on the
three mass-squared differences obtained from the analyses of the solar,
atmospheric and LSND data. If neutrinoless double -decay proceeds via
the mechanism involving , conclusions about neutrinoless double
-decay can be drawn. If one of the two viable four-neutrino schemes
(Scheme A) is realized in nature, can be as large as 1 eV and
neutrinoless double -decay could possibly be discovered in the near
future. In this case a Majorana CP phase of the mixing matrix could be
determined. In the other four-neutrino scheme (Scheme B) there is an upper
bound on of the order of eV. In the case of three-neutrino
mixing the same is true if the neutrino mass spectrum is hierarchical, however,
if there exist two quasi-degenerate neutrinos and the first neutrino has a much
smaller mass, values of as large as eV are possible.Comment: 15 pages, REVTEX, 2 figures, final version to be published in Phys.
Lett.
Neutrinoless double-beta decay with three or four neutrino mixing
Considering the scheme with mixing of three neutrinos and a mass hierarchy
that can accommodate the results of solar and atmospheric neutrino experiments,
it is shown that the results of solar neutrino experiments imply a lower bound
for the effective Majorana mass in neutrinoless double-beta decay, under the
natural assumptions that massive neutrinos are Majorana particles and there are
no unlikely fine-tuned cancellations among the contributions of the different
neutrino masses. Considering the four-neutrino schemes that can accommodate
also the results of the LSND experiment, it is shown that only one of them is
compatible with the results of neutrinoless double-beta decay experiments and
with the measurement of the abundances of primordial elements produced in
Big-Bang Nucleosynthesis. It is shown that in this scheme, under the
assumptions that massive neutrinos are Majorana particles and there are no
cancellations among the contributions of the different neutrino masses, the
results of the LSND experiment imply a lower bound for the effective Majorana
mass in neutrinoless double-beta decay.Comment: 18 pages including 2 figures, RevTe
Neutrino Oscillations in the Framework of Three-Generation Mixings with Mass Hierarchy
We have analyzed the results of reactor and accelerator neutrino oscillation
experiments in the framework of a general model with mixing of three neutrino
fields and a neutrino mass hierarchy that can accommodate the results of the
solar neutrino experiments. It is shown that
oscillations with and amplitude
larger than are not compatible with the existing limits on
neutrino oscillations if the non-diagonal elements of the mixing matrix and are small. Thus, if the
excess of electron events recently observed in the LSND experiment is due to oscillations, the mixing in the lepton sector
is basically different from the CKM mixing of quarks. If this type of mixing is
realized in nature, the observation of
oscillations would not influence
oscillations that are being searched for in the CHORUS and NOMAD experiments.Comment: Revtex file, 13 pages + 2 figures (included). The postscript file of
text and figures is available at
http://www.to.infn.it/teorici/giunti/papers.html or
ftp://ftp.to.infn.it/pub/giunti/1995/dftt-25-95/dftt-25-95.ps.
Neutrino masses and mixing from neutrino oscillation data
We discuss what information about the neutrino mass spectrum and the elements
of the neutrino mixing matrix can be inferred from the results of neutrino
oscillation experiments. The cases of three and four massive neutrinos are
considered. It is shown that the general characteristics of the neutrino mixing
matrix are quite different from those of the quark mixing matrix.Comment: 4 pages, including 2 figures. Talk presented by S.M. Bilenky at the
XVI International Workshop on Weak Interactions and Neutrinos, Capri, Italy,
June 22-28 199
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
We present a unified global analysis of neutrino oscillation data within the
framework of the four-neutrino mass schemes (3+1) and (2+2). We include all
data from solar and atmospheric neutrino experiments, as well as information
from short-baseline experiments including LSND. If we combine only solar and
atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas
short-baseline data in combination with atmospheric data prefers (2+2) models.
When combining all data in a global analysis the (3+1) mass scheme gives a
slightly better fit than the (2+2) case, though all four-neutrino schemes are
presently acceptable. The LSND result disfavors the three-active neutrino
scenario with only and at 99.9% CL with
respect to the four-neutrino best fit model. We perform a detailed analysis of
the goodness of fit to identify which sub-set of the data is in disagreement
with the best fit solution in a given mass scheme.Comment: 32 pages, 8 Figures included, REVTeX4.Improved discussion in sec. XI,
references added, version accepted by Phys. Rev.
Neutrino oscillation constraints on neutrinoless double beta decay
We have studied the constraints imposed by the results of neutrino
oscillation experiments on the effective Majorana mass || that characterizes
the contribution of Majorana neutrino masses to the matrix element of
neutrinoless double-beta decay. We have shown that in a general scheme with
three Majorana neutrinos and a hierarchy of neutrino masses (which can be
explained by the see-saw mechanism), the results of neutrino oscillation
experiments imply rather strong constraints on the parameter ||. From the
results of the first reactor long-baseline experiment CHOOZ and the Bugey
experiment it follows that || < 3x10^{-2} eV if the largest mass-squared
difference is smaller than 2 eV^2. Hence, we conclude that the observation of
neutrinoless double-beta decay with a probability that corresponds to || >
10^{-1} eV would be a signal for a non-hierarchical neutrino mass spectrum
and/or non-standard mechanisms of lepton number violation.Comment: 20 pages, including 4 figure
Lepton Mixing Matrix in Standard Model Extended by One Sterile Neutrino
We consider the simplest extension of the standard electroweak model by one
sterile neutrino that allows for neutrino masses and mixing. We find that its
leptonic sector contains much less free physical parameters than previously
realized. In addition to the two neutrino masses, the lepton mixing matrix in
charged current interactions involves (n-1) free physical mixing angles for n
generations. The mixing matrix in neutral current interactions of neutrinos is
completely fixed by the two masses. Both interactions conserve CP. We
illustrate the phenomenological implications of the model by vacuum neutrino
oscillations, tritium beta decay and neutrinoless double beta decay. It turns
out that, due to the revealed specific structure in its mixing matrix, the
model with any n generations cannot accommodate simultaneously the data by
KamLAND, K2K and CHOOZ.Comment: 14 pages, no figures; version 2: (1) added a short paragraph at the
end of subsec 2.2 to record the counting of physical parameters for any
numbers of generations and sterile neutrinos for completeness; (2) added a
note in ref list, item [18] to quote and comment on an earlier work; (3)
added the second paper to ref list, item [17]; (4) fixed typo
Statistical Analysis of Different Muon-antineutrino->Electron-antineutrino Searches
A combined statistical analysis of the experimental results of the LSND and
KARMEN \numubnueb oscillation search is presented. LSND has evidence for
neutrino oscillations that is not confirmed by the KARMEN experiment. This
joint analysis is based on the final likelihood results for both data sets. A
frequentist approach is applied to deduce confidence regions. At a combined
confidence level of 36%, there is no area of oscillation parameters compatible
with both experiments. For the complementary confidence of 1-0.36=64%, there
are two well defined regions of oscillation parameters (sin^2(2th),Dm^2)
compatible with both experiments.Comment: 25 pages, including 10 figures, submitted to Phys. Rev.
Long-baseline neutrino oscillation experiments and CP violation in the lepton sector
We discuss possibilities to investigate the effects of CP (and T) violation
in the lepton sector in neutrino oscillation experiments. We consider the
effects of CP violation in the framework of two schemes of mixing of four
massive neutrinos that can accommodate the results of all neutrino oscillation
experiments. Using the constraints on the mixing parameters that follow from
the results of short-baseline neutrino oscillation experiments, we derive
rather strong upper bounds on the effects of CP violation in nu_munu_e
transitions in long-baseline neutrino oscillation experiments. We show that the
effects of CP violation in nu_munu_tau transitions in long-baseline
oscillation experiments can be as large as is allowed by the unitarity of the
mixing matrix. The matter effects, which complicate the problem of searching
for CP violation in long-baseline experiments, are discussed in detail. We
consider the T-odd asymmetries whose measurement could allow to reveal T and CP
violation in the lepton sector independently from matter effects.Comment: 31 pages, including 5 figure
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