214 research outputs found
Berry Phase in Neutrino Oscillations
We study the Berry phase in neutrino oscillations for both Dirac and Majorana
neutrinos. In order to have a Berry phase, the neutrino oscillations must occur
in a varying medium, the neutrino-background interactions must depend on at
least two independent densities, and also there must be CP violation if the
neutrino interactions with matter are mediated only by the standard model W and
Z boson exchanges which implies that there must be at least three generations
of neutrinos. The CP violating Majorana phases do not play a role in generating
a Berry phase. We show that a natural way to satisfy the conditions for the
generation of a Berry phase is to have sterile neutrinos with active-sterile
neutrino mixing, in which case at least two active and one sterile neutrinos
are required. If there are additional new CP violating flavor changing
interactions, it is also possible to have a non-zero Berry phase with just two
generations.Comment: RevTex 16 pages, no figures, new discussions about sterile neutrino
added,typos corrected and errors in references correcte
Measurement of the solar neutrino capture rate with gallium metal
The solar neutrino capture rate measured by the Russian-American Gallium
Experiment (SAGE) on metallic gallium during the period January 1990 through
December 1997 is 67.2 (+7.2-7.0) (+3.5-3.0) SNU, where the uncertainties are
statistical and systematic, respectively. This represents only about half of
the predicted Standard Solar Model rate of 129 SNU. All the experimental
procedures, including extraction of germanium from gallium, counting of 71Ge,
and data analysis are discussed in detail.Comment: 34 pages including 14 figures, Revtex, slightly shortene
Confronting mass-varying neutrinos with MiniBooNE
We study the proposal that mass-varying neutrinos could provide an
explanation for the LSND signal for \bar\nu_mu to \bar\nu_e oscillations. We
first point out that all positive oscillation signals occur in matter and that
three active mass-varying neutrinos are insufficient to describe all existing
neutrino data including LSND. We then examine the possibility that a model with
four mass-varying neutrinos (three active and one sterile) can explain the LSND
effect and remain consistent with all other neutrino data. We find that such
models with a 3+1 mass structure in the neutrino sector may explain the LSND
data and a null MiniBooNE result for 0.10 < \sin^2 2\theta_x < 0.30.
Predictions of the model include a null result at Double-CHOOZ, but positive
signals for underground reactor experiments and for \nu_\mu to \nu_e
oscillations in long-baseline experiments.Comment: 22 pages, 3 figures, 1 table. Comment added about recent MINOS dat
Probing non-standard decoherence effects with solar and KamLAND neutrinos
It has been speculated that quantum gravity might induce a "foamy" space-time
structure at small scales, randomly perturbing the propagation phases of
free-streaming particles (such as kaons, neutrons, or neutrinos). Particle
interferometry might then reveal non-standard decoherence effects, in addition
to standard ones (due to, e.g., finite source size and detector resolution.) In
this work we discuss the phenomenology of such non-standard effects in the
propagation of electron neutrinos in the Sun and in the long-baseline reactor
experiment KamLAND, which jointly provide us with the best available probes of
decoherence at neutrino energies E ~ few MeV. In the solar neutrino case, by
means of a perturbative approach, decoherence is shown to modify the standard
(adiabatic) propagation in matter through a calculable damping factor. By
assuming a power-law dependence of decoherence effects in the energy domain
(E^n with n = 0,+/-1,+/-2), theoretical predictions for two-family neutrino
mixing are compared with the data and discussed. We find that neither solar nor
KamLAND data show evidence in favor of non-standard decoherence effects, whose
characteristic parameter gamma_0 can thus be significantly constrained. In the
"Lorentz-invariant" case n=-1, we obtain the upper limit gamma_0<0.78 x 10^-26
GeV at 95% C.L. In the specific case n=-2, the constraints can also be
interpreted as bounds on possible matter density fluctuations in the Sun, which
we improve by a factor of ~ 2 with respect to previous analyses.Comment: Minor changes. Version accepted for publication in Phys. Rev.
Lepton Numbers in the framework of Neutrino Mixing
In this short review we discuss the notion of lepton numbers. The strong
evidence in favor of neutrino oscillations obtained recently in the
Super-Kamiokande atmospheric neutrino experiment and in solar neutrino
experiments imply that the law of conservation of family lepton numbers L_e,
L_mu and L_tau is strongly violated. We consider the states of flavor neutrinos
nu_e, nu_mu and nu_tau and we discuss the evolution of these states in space
and time in the case of non-conservation of family lepton numbers due to the
mixing of light neutrinos. We discuss and compare different flavor neutrino
discovery experiments. We stress that experiments on the search for
nu_mu->nu_tau and nu_e->nu_tau oscillations demonstrated that the flavor
neutrino nu_tau is a new type of neutrino, different from nu_e and nu_mu. In
the case of neutrino mixing, the lepton number (only one) is connected with the
nature of massive neutrinos. Such conserved lepton number exist if massive
neutrinos are Dirac particles. We review possibilities to check in future
experiments whether the conserved lepton number exists.Comment: 20 page
Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis
We investigate the extent to which leptonic CP-violation in (3+2) sterile
neutrino models leads to different oscillation probabilities for
and oscillations at
MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation
results, including the LSND and null SBL results, to which we impose additional
constraints from atmospheric oscillation data. We obtain the favored regions in
MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2)
CP-violating models. We further investigate the allowed CP-violation phase
values and the MiniBooNE reach for such a CP violation measurement. The
analysis shows that the oscillation probabilities in MiniBooNE neutrino and
antineutrino running modes can differ significantly, with the latter possibly
being as much as three times larger than the first. In addition, we also show
that all possible values of the single CP-violation phase measurable at short
baselines in (3+2) models are allowed within 99% CL by existing data.Comment: Fixed a typo following PRD Erratum. 8 pages, 5 figure
Two Gallium data sets, spin flavour precession and KamLAND
We reexamine the possibility of a time modulation of the low energy solar
neutrino flux which is suggested by the average decrease of the Ga data in line
with our previous arguments. We perform two separate fits to the solar neutrino
data, one corresponding to 'high' and the other to 'low' Ga data, associated
with low and high solar activity respectively. We therefore consider an
alternative to the conventional solar+KamLAND fitting, which allows one to
explore the much wider range of the angle permitted by the
KamLAND fitting alone. We find a solution with parameters in which the 'high' and
the 'low' Ga rates lie far apart and are close to their central values and is
of comparable quality to the global best fit, where these rates lie much closer
to each other. This is an indication that the best fit in which all solar and
KamLAND data are used is not a good measure of the separation of the two Ga
data sets, as the information from the low energy neutrino modulation is
dissimulated in the wealth of data. Furthermore for the parameter set proposed
one obtains an equally good fit to the KamLAND energy spectrum and an even
better fit than the 'conventional' LMA one for the reactor antineutrino
survival probability as measured by KamLAND.Comment: V2: 15 pages, 3 eps figures, fit improved, final version to appear in
Journal of Physics
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