47 research outputs found
Unknowns after the SNO Charged-Current Measurement
We perform a model-independent analysis of solar neutrino flux rates
including the recent charged-current measurement at the Sudbury Neutrino
Observatory (SNO). We derive a universal sum rule involving SNO and
SuperKamiokande rates, and show that the SNO neutral-current measurement can
not fix the fraction of solar oscillating to sterile neutrinos. The
large uncertainty in the SSM B flux impedes a determination of the sterile
neutrino fraction.Comment: Version to appear in PRL; includes analysis with anticipated SNO NC
measuremen
Do experiments suggest a hierarchy problem?
The hierarchy problem of the scalar sector of the standard model is
reformulated, emphasizing the role of experimental facts that may suggest the
existence of a new physics large mass scale, for instance indications of the
instability of the matter, or indications in favor of massive neutrinos. In the
see-saw model for the neutrino masses a hierarchy problem arises if the mass of
the right-handed neutrinos is larger than approximatively GeV: this
problem, and its possible solutions, are discussed.Comment: revtex, 4 pages, 1 figur
See-saw mechanism and four light neutrino state
A formal proof is given that in a see-saw type neutrino mass matrix with only
two neutrino mass scales () and the maximal rank of , we
can not get a fourth light sterile neutrino.Comment: 5 page
Flavor Alignment in SUSY GUTs
A Supersymmetric Grand unified model is constructed based on SO(10)xSO(10)
symmetry in which new types of Yukawa matrices couple standard and exotic
fermions. Evolution of these couplings from the Grand Unified scale to the
electroweak scale causes some of them to be driven to their fixed points. This
solves the supersymmetric alignment problem and ensures that there are no
observable flavor changing neutral currents mediated by supersymmetric
particles. Fermion hierarchy and neutrino mixing constraints are automatically
satisfied in this formalism.Comment: 20 pages, 1 figur
Charged lepton Flavor Violation in Supersymmetry with Bilinear R-Parity Violation
The simplest unified extension of the Minimal Supersymmetric Standard Model
with bi-linear R-parity violation naturally predicts a hierarchical neutrino
mass spectrum, suitable to explain atmospheric and solar neutrino fluxes. We
study whether the individual violation of the lepton numbers L_{e,mu,tau} in
the charged sector can lead to measurable rates for BR(mu->e gamma)and
$BR(tau-> mu gamma). We find that some of the R-parity violating terms that are
compatible with the observed atmospheric neutrino oscillations could lead to
rates for mu->e gamma measurable in projected experiments. However, the Delta
m^2_{12} obtained for those parameters is too high to be compatible with the
solar neutrino data, excluding therefore the possibility of having measurable
rates for mu->e gamma in the model.Comment: 29 pages, 8 figures. Constraint from solar neutrino data included,
conclusions changed respect v
Can R-parity violation explain the LSND data as well?
The recent Super-Kamiokande data now admit only one type of mass hierarchy in
a framework with three active and one sterile neutrinos. We show that neutrino
masses and mixings generated by R-parity-violating couplings, with values
within their experimental upper limits, are capable of reproducing this
hierarchy, explaining all neutrino data particularly after including the LSND
results.Comment: 7 pages, Latex, 3 PS figures; in v2 a few clarifying remarks included
and two references added (to appear in Physical Review D
Lepton-flavor violating decays as probes of quantum gravity?
Lepton flavor violating decays and are considered. It is shown that these decays can reach sizeable
magnitudes if some specific lepton-flavor violating 4-fermion operators are
generated by low scale quantum gravity effects, or by some other new physics at
a TeV scale.Comment: 18 pages, 1 figures, LaTeX, uses FEYNMAN package. New references
adde
New interactions in neutrino oscillations with three light flavors
If one assumes solar and LSND neutrino oscillations to explain the
corresponding data, then the atmospheric neutrino deficit cannot be
accommodated within the Standard Model with three light flavors, unless one
ignores the data's zenith-angle dependence. We propose a novel solution to this
problem by postulating large anomalous diagonal -quark interactions
which affect oscillations traversing the Earth and induce
the observed zenith-angle dependence.Comment: Final version, to appear in Phys. Rev. Letters dated May 25, 199
The hidden sterile neutrino and the (2+2) sum rule
We discuss oscillations of atmospheric and solar neutrinos into sterile
neutrinos in the 2+2 scheme. A zeroth order sum rule requires equal
probabilities for oscillation into nu_s and nu_tau in the solar+atmospheric
data sample. Data does not favor this claim. Here we use scatter plots to
assess corrections of the zeroth order sum rule when (i) the 4 x 4 neutrino
mixing matrix assumes its full range of allowed values, and (ii) matter effects
are included. We also introduce a related "product rule". We find that the sum
rule is significantly relaxed, due to both the inclusion of the small mixing
angles (which provide a short-baseline contribution) and to matter effects. The
product rule is also dramatically altered. The observed relaxation of the sum
rule weakens the case against the 2+2 model and the sterile neutrino. To
invalidate the 2+2 model, a global fit to data with the small mixing angles
included seems to be required.Comment: 43 pages, 11 figures (same as v2, accidental replacement
Update on neutrino mixing in the early Universe
From the current cosmological observations of CMB and nuclear abundances we
show, with an analytic procedure, that the total effective number of extra
neutrino species . We also describe the possible
signatures of non standard effects that could be revealed in future CMB
observations. This cosmological information is then applied to neutrino mixing
models. Taking into account the recent results from the SNO and SuperKamiokande
experiments, disfavouring pure active to sterile neutrino oscillations, we show
that all 4 neutrino mixing models, both of 2+2 and 3+1 type, lead to a full
thermalization of the sterile neutrino flavor. Moreover such a sterile neutrino
production excludes the possibility of an electron neutrino asymmetry
generation and we conclude that , in
disagreement with the cosmological bound. This result is valid under the
assumption that the initial neutrino asymmetries are small. We suggest the
existence of a second sterile neutrino flavor, with mixing properties such to
generate a large electron neutrino asymmetry, as a possible way out.Comment: 29 pages, 3 figures; to appear on Phys.Rev.D; added discussion (at
page 19) and references; typos correcte