1,462 research outputs found
Test of non-standard neutrino properties with the BOREXINO source experiments
We calculate the event rates induced by high-intensity radioactive sources of
nu_e (51Cr) and of anti-nu_e (90Sr), to be located near the BOREXINO detector.
Calculations are performed both in the standard case and assuming non-standard
properties of neutrinos, including flavor oscillations, neutrino
electromagnetic interactions, and deviations from the standard vector and axial
couplings in the nu_e-e interaction. It is shown that, in some cases, the
current limits on non-standard neutrino properties can be significantly
improved.Comment: 15 pages (RevTeX) + 4 figures (postscript) included with epsfig.sty.
Minor changes and corrections, 3 references added. Final version to be
published in Europ. Phys. Jour.
Neutrino masses and mixings: Status of known and unknown parameters
Within the standard 3nu mass-mixing framework, we present an up-to-date
global analysis of neutrino oscillation data (as of January 2016), including
the latest available results from experiments with atmospheric neutrinos
(Super-Kamiokande and IceCube DeepCore), at accelerators (first T2K anti-nu and
NOvA nu runs in both appearance and disappearance mode), and at short-baseline
reactors (Daya Bay and RENO far/near spectral ratios), as well as a reanalysis
of older KamLAND data in the light of the "bump" feature recently observed in
reactor spectra. We discuss improved constraints on the five known oscillation
parameters (delta m^2, |Delta m^2|, sin^2theta_12, sin^2theta_13,
sin^2theta_23), and the status of the three remaining unknown parameters: the
mass hierarchy, the theta_23 octant, and the possible CP-violating phase delta.
With respect to previous global fits, we find that the reanalysis of KamLAND
data induces a slight decrease of both delta m^2 and sin^2theta_12, while the
latest accelerator and atmospheric data induce a slight increase of |Delta
m^2|. Concerning the unknown parameters, we confirm the previous intriguing
preference for negative values of sin(delta) [with best-fit values around
sin(delta) ~ -0.9], but we find no statistically significant indication about
the theta_23 octant or the mass hierarchy (normal or inverted). Assuming an
alternative (so-called LEM) analysis of NOvA data, some delta ranges can be
excluded at >3 sigma, and the normal mass hierarchy appears to be slightly
favored at 90% C.L. We also describe in detail the covariances of selected
pairs of oscillation parameters. Finally, we briefly discuss the implications
of the above results on the three non-oscillation observables sensitive to the
(unknown) absolute nu mass scale: the sum of nu masses, the effective nu_e
mass, and the effective Majorana mass.Comment: 15 pages, 9 figures, 2 tables. Invited contribution prepared for the
Nuclear Physics B Special Issue on "Neutrino Oscillations" celebrating the
Nobel Prize in Physics 201
Zenith distribution of atmospheric neutrino events and electron neutrino mixing
Assuming atmospheric neutrino oscillations with dominant nu_munu_tau
transitions, we discuss how subdominant nu_e mixing (within the Chooz reactor
bounds) can alter the zenith distributions of neutrino-induced electrons and
muons. We isolate two peculiar distortion effects, one mainly related to nu_e
mixing in vacuum and the other to matter oscillations, that may be sufficiently
large to be detected by the SuperKamiokande atmospheric nu experiment. These
effects (absent for pure two-flavor nu_munu_tau transitions) do not vanish
in the limit of energy-averaged oscillations.Comment: 6 pages, RevTeX, no figure
Analysis of energy- and time-dependence of supernova shock effects on neutrino crossing probabilities
It has recently been realized that supernova neutrino signals may be affected
by shock propagation over a time interval of a few seconds after bounce. In the
standard three-neutrino oscillation scenario, such effects crucially depend on
the neutrino level crossing probability P_H in the 1-3 sector. By using a
simplified parametrization of the time-dependent supernova radial density
profile, we explicitly show that simple analytical expressions for P_H
accurately reproduce the phase-averaged results of numerical calculations in
the relevant parameter space. Such expressions are then used to study the
structure of P_H as a function of energy and time, with particular attention to
cases involving multiple crossing along the shock profile. Illustrative
applications are given in terms of positron spectra generated by supernova
electron antineutrinos through inverse beta decay.Comment: Major changes both in the text and in the figures in order to include
the effect of a step-like shock front density profile; final version to
appear in Physical Review
Addendum to: Model-dependent and -independent implications of the first Sudbury Neutrino Observatory results
In the light of recent experimental and theoretical improvements, we review
our previous model-independent comparison [hep-ph/0106247] of the
Super-Kamiokande (SK) and Sudbury Neutrino Observatory (SNO) solar neutrino
event rates, including updated values for the ``equalized'' SK datum and for
the reference Standard Solar Model (SSM) B neutrino flux. We find that the
joint SK+SNO evidence for active neutrino flavor transitions is confirmed at
the level of 3.3 standard deviations, independently of possible transitions to
sterile states. Barring sterile neutrinos, we estimate the 3-sigma range for
the B neutrino flux (normalized to SSM) as f_B=0.96 +0.54-0.55.
Accordingly, the 3-sigma range for the energy-averaged nu_e survival
probability is found to be = 0.31 +0.55-0.16, independently of the
functional form of P_ee. An increase of the reference nu_e + d --> p + p + e
cross section by ~3%, as suggested by recent theoretical calculations, would
slightly shift the central values of f_B and of to ~1.00 and ~0.29,
respectively, and would strengthen the model-independent evidence for nu_e
transitions into active states at the level of ~3.6 sigma.Comment: 6 pages + 2 figures. Addendum to hep-ph/010624
Atmospheric, Solar, and CHOOZ neutrinos: a global three generation analysis
We perform a global three generation analysis of the current solar and
atmospheric evidence in favor of neutrino oscillations. We also include the
negative results coming from CHOOZ to constrain the nu_e mixing. We study the
zones of mass-mixing oscillations parameters compatible with all the data. It
is shown that almost pure nu_mu nu_tau oscillations are required to
explain the atmospheric neutrino anomaly and almost pure nu_1 nu_2
oscillations to account for the solar neutrino deficit.Comment: 4 pages, talk given at 36th Rencontres de Moriond: Electroweak
Interactions and Unified Theories, Les Arcs, France, 10-17 Mar 200
Probing supernova shock waves and neutrino flavor transitions in next-generation water-Cherenkov detectors
Several current projects aim at building a large water-Cherenkov detector,
with a fiducial volume about 20 times larger than in the current
Super-Kamiokande experiment. These projects include the Underground nucleon
decay and Neutrino Observatory (UNO) in the Henderson Mine (Colorado), the
Hyper-Kamiokande (HK) detector in the Tochibora Mine (Japan), and the MEgaton
class PHYSics (MEMPHYS) detector in the Frejus site (Europe). We study the
physics potential of a reference next-generation detector (0.4 Mton of fiducial
mass) in providing information on supernova neutrino flavor transitions with
unprecedented statistics. After discussing the ingredients of our calculations,
we compute neutrino event rates from inverse beta decay (), elastic scattering on electrons, and scattering on oxygen, with emphasis on
their time spectra, which may encode combined information on neutrino
oscillation parameters and on supernova forward (and possibly reverse) shock
waves. In particular, we show that an appropriate ratio of low-to-high energy
events can faithfully monitor the time evolution of the neutrino crossing
probability along the shock-wave profile. We also discuss some background
issues related to the detection of supernova relic neutrinos, with and without
the addition of gadolinium.Comment: Revised version (27 pages, 13 eps figures), to appear in JCAP.
Includes revised numerical estimates and figures. In particular: calculations
of inverse beta decay event rates improved by using the differential cross
section by Vissani and Strumia (astro-ph/0302055); supernova relic neutrino
flux calculations updated by using recent GALEX Mission data
(astro-ph/0411424) on the star formation rate (SFR). References added.
Conclusions unchange
Status of three-neutrino oscillation parameters, circa 2013
The standard three-neutrino (3nu) oscillation framework is being increasingly
refined by results coming from different sets of experiments, using neutrinos
from solar, atmospheric, accelerator and reactor sources. At present, each of
the known oscillation parameters [the two squared mass gaps (delta m^2, Delta
m^2) and the three mixing angles (theta_12}, theta_13, theta_23)] is dominantly
determined by a single class of experiments. Conversely, the unknown parameters
[the mass hierarchy, the theta_23 octant and the CP-violating phase delta] can
be currently constrained only through a combined analysis of various
(eventually all) classes of experiments. In the light of recent new results
coming from reactor and accelerator experiments, and of their interplay with
solar and atmospheric data, we update the estimated N-sigma ranges of the known
3nu parameters, and revisit the status of the unknown ones. Concerning the
hierarchy, no significant difference emerges between normal and inverted mass
ordering. A slight overall preference is found for theta_23 in the first octant
and for nonzero CP violation with sin delta < 0; however, for both parameters,
such preference exceeds 1 sigma only for normal hierarchy. We also discuss the
correlations and stability of the oscillation parameters within different
combinations of data sets.Comment: Updated and revised version, accepted for publication in PRD. The
analysis includes the latest (March 2014) T2K disappearance data: all the
figures and the numerical results have been updated, and parts of the text
have been revised accordingl
The inclusion of the epithelium in numerical models of the human cornea
We present a patient-specific finite element model of the human cornea that
accounts for the presence of the epithelium. The thin anterior layer that protects
the cornea from the external actions has a scant relevance from the mechanical
point of view and it has been neglected in most numerical models of the cornea,
which assign to the entire cornea the mechanical properties of the stroma. Yet,
modern corneal topographers capture the geometry of the epithelium, which can
be naturally included into a patient-specific solid model of the cornea, treated as
a multi-layer solid. For numerical applications, the presence of a thin layer on the
anterior cornea requires a finer discretization and the definition of two constitutive
models (including the corresponding properties) for stroma and epithelium. In
this study we want to assess the relevance of the inclusion of the epithelium in
the model of the cornea, by analyzing the effects in terms of uncertainties of
the mechanical properties, stress distribution across the thickness and numerical
discretization
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