25 research outputs found
Physics potentials of pp and pep solar neutrino fluxes
Experimental determinations of the pp and pep fluxes have great
potentialities. We briefly review the reasons that make such measurements
privileged tests of neutrino properties. We discuss the predictions for these
fluxes given by four good solutions to the solar neutrino problem: small- and
large-angle MSW and Just-So oscillations into active neutrinos, and small-angle
MSW oscillations into sterile neutrinos. In addition, we examine the impact of
the planned Hellaz detector, which should measure separately the nu_e and nu_mu
fluxes in the pp energy window and the signal from the pep neutrinos, for
distinguishing among the different solutions and for determining the solar
central temperature.Comment: 14 pages, ReVTeX, plus 9 postscript figure
The Cr neutrino source and Borexino: a desirable marriage
Exposure to a Cr neutrino source as that used in Gallex will provide
an excellent overall performance test of Borexino, which should collect about
1400 source induced events, with an initial rate of about 35 counts per day.
This will be particularly important if MSW-small-angle turns out to be the
solution of the solar neutrino problem. In addition, if an independent,
accurate calibration is available, one will have an interesting experiment on
neutrino properties: as an example, a neutrino magnetic moment of the order
could be detected/excluded at the 90\% C.L.Comment: 7 pages, RevTeX, plus 3 postscripts figures, tarred, compresse
Effects for atmospheric neutrino experiments from electron neutrino oscillations
The minimal interpretation of the atmospheric neutrino data suggests that the
muon neutrino oscillates into another species with a mixing angle close to the
maximal . In the Exact Parity Symmetric Model, both the muon and
electron neutrinos are expected to be maximally mixed with essentially sterile
partners ( and respectively). We examine the impact of
maximal oscillations on the atmospheric neutrino experiments.
We estimate that maximal oscillations will have effects on
atmospheric neutrino data for . For in this range, a slight but distinctive rise in the
ratio of muon-like to electron-like events is predicted for the low-energy
sample. Furthermore, the ratio of low-energy electron-like events with zenith
angles less than to those with zenith angles greater than
should be greater than 1.Comment: 11 pages, LaTeX, no figure
Last Hope for an astrophysical solution to the solar neutrino problem
We discuss what appears the last hope for an astrophysical solution to the
solar neutrino problem: a correlated variation of the astrophysical factors for
the helium burning cross sections ( and ) and either
or the central temperature . In this context, we recognize the important
role played by the CNO neutrinos. In fact, we can obtain a fair fit to the
experimental data only if three conditions are met simultaneously: the
astrophysical factor is about 200 times what is presently estimated,
the astrophysical factor is about 3 times larger and the N and
O neutrino fluxes are negligible compared to the ones predicted by
standard solar models. These conditions are not supported by the present data
and their correlated combination is improbable.Comment: 11 pages, ReVTeX, plus 3 figures added as uuencoded compressed
postscript files. The postscript file with the text and 3 figures is
available at ftp://risc0.ca.infn.it/pub/private/lissia/infnca-th9511.p
Resonance spin flavour precession and solar neutrinos
We examine the prospects for the resonance spin flavour precession as a
solution to the solar neutrino problem. We study seven different realistic
solar magnetic field profiles and, by numerically integrating the evolution
equations, perform a fit of the event rates for the three types of solar
neutrino experiments (Ga, Cl and SuperKamiokande) and a fit of the energy
spectrum of the recoil electrons in SuperKamiokande. A analysis shows
that the quality of the rate fits is excellent for two of the field profiles
and good for all others with always well below unity.
Regarding the fits for the energy spectrum, their quality is better than that
for the small mixing angle MSW solution of the solar neutrino problem, at the
same level as that for the large mixing angle MSW solution but worse than that
for the vacuum oscillations one. The experimental data on the spectrum are
however largely uncertain especially in the high energy sector, so that it is
too early yet to draw any clear conclusions on the likeliest type of particle
physics solution to the solar neutrino problem.Comment: LaTeX, 30 pages, 12 figures. A few typos corrected. Final version to
be published in Astropart. Phy
Just-So Oscillation: as Just as MSW?
The neutrino long wavelength (just-so) oscillation is reconsidered as a
solution to the solar neutrino problem. In the light of the presently updated
results of the four solar neutrino experiments, the data fit in the just-so
scenario substantially improves and becomes almost as good as in the MSW
scenario. Surprising result of our analysis is that best fit is achieved when
the oscillation occurs only between two neutrino states: switching on the
oscillation into third neutrino increases the value. Namely, we
consider the vacuum oscillation scenario in the three-neutrino system (4
parameters) and find out that the minimum is always achieved in the
{\it two} parameter subspace in which actually only {\it two} neutrino states
oscillate. This holds in the framework of any solar model with relaxed
prediction of the various neutrino fluxes. The possible theoretical
implications of this observation are also discussed.Comment: 9 pages, Latex, 4 figures (not included, available upon request from
[email protected]
Asymmetric Inflationary Reheating and the Nature of Mirror Universe
The existence of a shadow world (or mirror universe) with matter and forces
identical to that of the visible world but interacting with the latter only via
gravity can be motivated by superstring theories as well as by recent attempts
to understand the nature of a sterile neutrino needed if all known neutrino
data are to be consistent with each other. A simple way to reconcile the
constraints of big bang nucleosynthesis in such a theory is to postulate that
the reheating temperature after inflation in the mirror universe is lower than
that in the visible one. We have constructed explicit models that realize this
proposal and have shown that the asymmetric reheating can be related to a
difference of the electroweak symmetry breaking scales in the two sectors,
which is needed for a solution of the neutrino puzzles in this picture.
Cosmological implications of the mirror matter are also discussed.Comment: 13 pages, LATEX, no figures (slight textual changes, few references
added
Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data
Motivated by the Exact Parity Model and other theories, the hypothesis that
each of the known neutrinos oscillates maximally with a sterile partner has
been put forward as an explanation of the atmospheric and solar neutrino
anomalies. We provide detailed predictions for muon and electron flux ratios
induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric
neutrinos. Several different, carefully chosen cuts on momentum and zenith
angle are proposed, emphasizing the role of up-down flux asymmetries.Comment: LaTeX, 8 figures, 17 pages, version to appear in Phys. Rev. D Rapid
Communication
Just So? Vacuum Oscillations and MSW: An Update
We find that vacuum oscillations (VO), large-mixing-angle and
small-mixing-angle MSW solutions to the solar neutrino problem (SNP) give all
very good fits to the most recent results. Measurements of the Be flux can,
in some cases, discriminate between different solutions to the SNP; in
particular, VO allow Be fluxes almost as large as the one predicted by the
SSM. We find that no evidence for seasonal variations can be extracted from
present data, but that the large statistics of SuperKamiokande should make
possible to study a significant portion of the presently allowed parameter
space by just looking for seasonal variations. We also discuss the Borexino
potential for detecting seasonal variations, which looks really impressive.Comment: 21 pages, ReVTeX, 15 figures as uuencoded compressed postscript
files. The postscript file with the text and 14 figures (no figure 4) is
available at ftp://risc0.ca.infn.it/pub/private/lissia/infncath9512.ps . To
appear in Astroparticle Physic