39 research outputs found
The likelihood for supernova neutrino analyses
We derive the event-by-event likelihood that allows to extract the complete
information contained in the energy, time and direction of supernova neutrinos,
and specify it in the case of SN1987A data. We resolve discrepancies in the
previous literature, numerically relevant already in the concrete case of
SN1987A data.Comment: 7 pages, 2 figures. Accepted for publication in PR
Which solar neutrino data favour the LMA solution?
Assuming neutrino oscillations, global analyses of solar data find that the
LOW solution is significantly disfavoured, leaving LMA as the best solution.
But the preference for LMA rests on three weak hints: the spectrum of earth
matter effects (Super-Kamiokande sees an overall day/night asymmetry only at 1
sigma), the Cl rate (but LMA and LOW predictions are both above the measured
value), the Ga rate (newer data decrease towards the LOW predictions both in
GNO and SAGE). Only new data will tell us if LMA is the true solution.Comment: 4 pages, 2 figure
Screening of Dirac flavor structure in the seesaw and neutrino mixing
We consider the mechanism of screening of the Dirac flavor structure in the
context of the double seesaw mechanism. As a consequence of screening, the
structure of the light neutrino mass matrix, m_\nu, is determined essentially
by the structure of the (Majorana) mass matrix, M_S, of new super-heavy (Planck
scale) neutral fermions S. We calculate effects of the renormalization group
running in order to investigate the stability of the screening mechanism with
respect to radiative corrections. We find that screening is stable in the
supersymmetric case, whereas in the standard model it is unstable for certain
structures of M_S. The screening mechanism allows us to reconcile the
(approximate) quark-lepton symmetry and the strong difference of the mixing
patterns in the quark and lepton sectors. It opens new possibilities to explain
a quasi-degenerate neutrino mass spectrum, special ``neutrino'' symmetries and
quark-lepton complementarity. Screening can emerge from certain flavor
symmetries or Grand Unification.Comment: 27 pages, 3 figures; references added, discussion of the E6 model
modifie
Large and Almost Maximal Neutrino Mixing within the Type II See-Saw Mechanism
Within the type II see-saw mechanism the light neutrino mass matrix is given
by a sum of a direct (or triplet) mass term and the conventional (type I)
see-saw term. Both versions of the see-saw mechanism explain naturally small
neutrino masses, but the type II scenario offers interesting additional
possibilities to explain large or almost maximal or vanishing mixings which are
discussed in this paper. We first introduce ``type II enhancement'' of neutrino
mixing, where moderate cancellations between the two terms can lead to large
neutrino mixing even if all individual mass matrices and terms generate small
mixing. However, nearly maximal or vanishing mixings are not naturally
explained in this way, unless there is a certain initial structure (symmetry)
which enforces certain elements of the matrices to be identical or related in a
special way. We therefore assume that the leading structure of the neutrino
mass matrix is the triplet term and corresponds to zero U_{e3} and maximal
theta_{23}. Small but necessary corrections are generated by the conventional
see-saw term. Then we assume that one of the two terms corresponds to an
extreme mixing scenario, such as bimaximal or tri-bimaximal mixing. Deviations
from this scheme are introduced by the second term. One can mimic Quark-Lepton
Complementarity in this way. Finally, we note that the neutrino mass matrix for
tri-bimaximal mixing can be -- depending on the mass hierarchy -- written as a
sum of two terms with simple structure. Their origin could be the two terms of
type II see-saw.Comment: 25 pages. Comments and references added, to appear in JHE
Baryogenesis via Leptogenesis in Adjoint SU(5)
The possibility to explain the baryon asymmetry in the Universe through the
leptogenesis mechanism in the context of Adjoint SU(5) is investigated. In this
model the neutrino masses are generated through the Type I and Type III seesaw
mechanisms, and the field responsible for the Type III seesaw, called rho_3,
generates the B-L asymmetry needed to satisfy the observed value of the baryon
asymmetry in the Universe. We find that the CP asymmetry originates only from
the vertex correction, since the self-energy contribution is not present. When
neutrino masses have a normal hierarchy, successful leptogenesis is possible
for 10^{11} GeV < M_{\rho_3}^{NH} < 4 10^{14} GeV. When the neutrino hierarchy
is inverted, the allowed mass range changes to 2 10^{11} GeV < M_{\rho_3}^{IH}
< 5 10^{11} GeV. These constraints make possible to rule out a large part of
the parameter space in the theory which was allowed by the unification of gauge
interactions and the constraints coming from proton decay.Comment: 15 pages, 3 figures, minor corrections, to appear in JCA
Overconstrained estimates of neutrinoless double beta decay within the QRPA
Estimates of nuclear matrix elements for neutrinoless double beta decay
(0nu2beta) based on the quasiparticle random phase approximations (QRPA) are
affected by theoretical uncertainties, which can be substantially reduced by
fixing the unknown strength parameter g_pp of the residual particle-particle
interaction through one experimental constraint - most notably through the
two-neutrino double beta decay (2nu2beta) lifetime. However, it has been noted
that the g_pp adjustment via 2\nu2\beta data may bring QRPA models in
disagreement with independent data on electron capture (EC) and single beta
decay (beta^-) lifetimes. Actually, in two nuclei of interest for 0nu2beta
decay (Mo-100 and Cd-116), for which all such data are available, we show that
the disagreement vanishes, provided that the axial vector coupling g_A is
treated as a free parameter, with allowance for g_A<1 (``strong quenching'').
Three independent lifetime data (2nu2beta, EC, \beta^-) are then accurately
reproduced by means of two free parameters (g_pp, g_A), resulting in an
overconstrained parameter space. In addition, the sign of the 2nu2beta matrix
element M^2nu is unambiguously selected (M^2nu>0) by the combination of all
data. We discuss quantitatively, in each of the two nuclei, these
phenomenological constraints and their consequences for QRPA estimates of the
0nu2beta matrix elements and of their uncertainties.Comment: Revised version (27 pages, including 10 figures), focussed on Mo-100
and Cd-116. To appear in J. Phys. G: Nucl. Phys. (2008
Study of the effect of neutrino oscillation on the supernova neutrino signal with the LVD detector
We present an update of our previous study (astro-ph/0112312) on how
oscillations affect the signal from a supernova core collapse observed in the
LVD detector at LNGS. In this paper we use a recent, more precise determination
of the cross section (astro-ph/0302055) to calculate the expected number of
inverse beta decay events, we introduce in the simulation also the -{\rm
Fe} interactions, we include the Earth matter effects and, finally, we study
also the inverted mass hierarchy case.Comment: 4 pages, 4 figures, to appear in the Proceedings of ICRC 200
Searching for prompt signatures of nearby core-collapse supernovae by a joint analysis of neutrino and gravitational-wave data
We discuss the science motivations and prospects for a joint analysis of
gravitational-wave (GW) and low-energy neutrino data to search for prompt
signals from nearby supernovae (SNe). Both gravitational-wave and low-energy
neutrinos are expected to be produced in the innermost region of a
core-collapse supernova, and a search for coincident signals would probe the
processes which power a supernova explosion. It is estimated that the current
generation of neutrino and gravitational-wave detectors would be sensitive to
Galactic core-collapse supernovae, and would also be able to detect
electromagnetically dark SNe. A joint GW-neutrino search would enable
improvements to searches by way of lower detection thresholds, larger distance
range, better live-time coverage by a network of GW and neutrino detectors, and
increased significance of candidate detections. A close collaboration between
the GW and neutrino communities for such a search will thus go far toward
realizing a much sought-after astrophysics goal of detecting the next nearby
supernova.Comment: 10 pages, 3 figures. To appear in Class. Quantum Gra
Neutrino Mixing and Neutrino Telescopes
Measuring flux ratios of ultra-high energy neutrinos is an alternative method
to determine the neutrino mixing angles and the CP phase delta. We conduct a
systematic analysis of the neutrino mixing probabilities and of various flux
ratios measurable at neutrino telescopes. The considered cases are neutrinos
from pion, neutron and muon-damped sources. Explicit formulae in case of mu-tau
symmetry and its special case tri-bimaximal mixing are obtained, and the
leading corrections due to non-zero theta_{13} and non-maximal theta_{23} are
given. The first order correction is universal as it appears in basically all
ratios. We study in detail its dependence on theta_{13}, theta_{23} and the CP
phase, finding that the dependence on theta_{23} is strongest. The flavor
compositions for the considered neutrino sources are evaluated in terms of this
correction. A measurement of a flux ratio is a clean measurement of the
universal correction (and therefore of theta_{13}, theta_{23} and delta) if the
zeroth order ratio does not depend on theta_{12}. This favors pion sources over
the other cases, which in turn are good candidates to probe theta_{12}. The
only situations in which the universal correction does not appear are certain
ratios in case of a neutron and muon-damped source, which depend mainly on
theta_{12} and receive only quadratic corrections from the other parameters. We
further show that there are only two independent neutrino oscillation
probabilities, give the allowed ranges of the considered flux ratios and of all
probabilities, and show that none of the latter can be zero or one.Comment: 29 pages, 8 figures. Minor changes, to appear in JCA
Study of the effect of neutrino oscillations on the supernova neutrino signal in the LVD detector
The LVD detector, located in the INFN Gran Sasso National Laboratory (Italy),
studies supernova neutrinos through the interactions with protons and carbon
nuclei in the liquid scintillator and interactions with the iron nuclei of the
support structure. We investigate the effect of neutrino oscillations in the
signal expected in the LVD detector. The MSW effect has been studied in detail
for neutrinos travelling through the collapsing star and the Earth. We show
that the expected number of events and their energy spectrum are sensitive to
the oscillation parameters, in particular to the mass hierarchy and the value
of , presently unknown. Finally we discuss the astrophysical
uncertainties, showing their importance and comparing it with the effect of
neutrino oscillations on the expected signal.Comment: Accepted for pubblication on Astroparticle Physics. 36 pages, 18
figure