100 research outputs found
Non-adiabatic level crossing in (non-) resonant neutrino oscillations
We study neutrino oscillations and the level-crossing probability
P_{LZ}=\exp(-\gamma_n\F_n\pi/2) in power-law like potential profiles
. After showing that the resonance point coincides only for a
linear profile with the point of maximal violation of adiabaticity, we point
out that the ``adiabaticity'' parameter can be calculated at an
arbitrary point if the correction function \F_n is rescaled appropriately. We
present a new representation for the level-crossing probability,
P_{LZ}=\exp(-\kappa_n\G_n), which allows a simple numerical evaluation of
in both the resonant and non-resonant cases and where \G_n contains
the full dependence of on the mixing angle . As an application
we consider the case important for oscillations of supernova neutrinos.Comment: 4 pages, revtex, 3 eps figure
Flavour-dependent radiative correction to neutrino-neutrino refraction
In the framework of the Standard Model we calculate the flavour non-universal
correction for neutrino refraction in a neutrino background and verify a
similar previous result for the case of ordinary-matter background. The
dominant term arises at loop level and involves tau leptons circulating in the
loop. These O(G_F m_tau^2) corrections to the tree-level potential provide the
dominant refractive difference between nu_mu and nu_tau unless the medium
contains mu or tau leptons. Our results affect the flavour evolution of dense
neutrino gases and may be of interest for collective three-flavour oscillations
of supernova neutrinos. We spell out explicitly how these non-universal
neutrino-neutrino interactions enter the flavour oscillation equations.Comment: 15 pages, 6 figures; updated reference lis
Supernova neutrino three-flavor evolution with dominant collective effects
Neutrino and antineutrino fluxes from a core-collapse galactic supernova are
studied, within a representative three-flavor scenario with inverted mass
hierarchy and tiny 1-3 mixing. The initial flavor evolution is dominated by
collective self-interaction effects, which are computed in a full three-family
framework along an averaged radial trajectory. During the whole time span
considered (t=1-20 s), neutrino and antineutrino spectral splits emerge as
dominant features in the energy domain for the final, observable fluxes. Some
minor or unobservable three-family features (e.g., related to the
muonic-tauonic flavor sector) are also discussed for completeness. The main
results can be useful for SN event rate simulations in specific detectors.Comment: 22 pages, including 9 figures (1 section with 3 figures added).
Accepted for publication in JCA
Neutrino oscillations in magnetically driven supernova explosions
We investigate neutrino oscillations from core-collapse supernovae that
produce magnetohydrodynamic (MHD) explosions. By calculating numerically the
flavor conversion of neutrinos in the highly non-spherical envelope, we study
how the explosion anisotropy has impacts on the emergent neutrino spectra
through the Mikheyev-Smirnov-Wolfenstein effect. In the case of the inverted
mass hierarchy with a relatively large theta_(13), we show that survival
probabilities of electron type neutrinos and antineutrinos seen from the
rotational axis of the MHD supernovae (i.e., polar direction), can be
significantly different from those along the equatorial direction. The event
numbers of electron type antineutrinos observed from the polar direction are
predicted to show steepest decrease, reflecting the passage of the
magneto-driven shock to the so-called high-resonance regions. Furthermore we
point out that such a shock effect, depending on the original neutrino spectra,
appears also for the low-resonance regions, which leads to a noticeable
decrease in the electron type neutrino signals. This reflects a unique nature
of the magnetic explosion featuring a very early shock-arrival to the resonance
regions, which is in sharp contrast to the neutrino-driven delayed supernova
models. Our results suggest that the two features in the electron type
antineutrinos and neutrinos signals, if visible to the Super-Kamiokande for a
Galactic supernova, could mark an observational signature of the magnetically
driven explosions, presumably linked to the formation of magnetars and/or
long-duration gamma-ray bursts.Comment: 25 pages, 21 figures, JCAP in pres
The neutrino signal at HALO: learning about the primary supernova neutrino fluxes and neutrino properties
Core-collapse supernova neutrinos undergo a variety of phenomena when they
travel from the high neutrino density region and large matter densities to the
Earth. We perform analytical calculations of the supernova neutrino fluxes
including collective effects due to the neutrino-neutrino interactions, the
Mikheev-Smirnov-Wolfenstein (MSW) effect due to the neutrino interactions with
the background matter and decoherence of the wave packets as they propagate in
space. We predict the numbers of one- and two-neutron charged and
neutral-current electron-neutrino scattering on lead events. We show that, due
to the energy thresholds, the ratios of one- to two-neutron events are
sensitive to the pinching parameters of neutrino fluxes at the neutrinosphere,
almost independently of the presently unknown neutrino properties. Besides,
such events have an interesting sensitivity to the spectral split features that
depend upon the presence/absence of energy equipartition among neutrino
flavors. Our calculations show that a lead-based observatory like the Helium
And Lead Observatory (HALO) has the potential to pin down important
characteristics of the neutrino fluxes at the neutrinosphere, and provide us
with information on the neutrino transport in the supernova core.Comment: 30 pages, 12 figures, 6 tables, minor correction
An accurate analytic description of neutrino oscillations in matter
A simple closed-form analytic expression for the probability of two-flavour
neutrino oscillations in a matter with an arbitrary density profile is derived.
Our formula is based on a perturbative expansion and allows an easy calculation
of higher order corrections. The expansion parameter is small when the density
changes relatively slowly along the neutrino path and/or neutrino energy is not
very close to the Mikheyev-Smirnov-Wolfenstein (MSW) resonance energy. Our
approximation is not equivalent to the adiabatic approximation and actually
goes beyond it. We demonstrate the validity of our results using a few model
density profiles, including the PREM density profile of the Earth. It is shown
that by combining the results obtained from the expansions valid below and
above the MSW resonance one can obtain a very good description of neutrino
oscillations in matter in the entire energy range, including the resonance
region.Comment: 16 pages,6 figure
Determination of the neutrino mass hierarchy in the regime of small matter effect
We point out a synergy between T-conjugated oscillation channels in the
determination of the neutrino mass hierarchy with oscillation experiments with
relatively short baselines (L < 700 km), where the matter effect is small. If
information from all four oscillation channels ,
, and is
available, a matter effect of few percent suffices to break the sign-degeneracy
and allows to determine the neutrino mass hierarchy. The effect is discussed by
analytical considerations of the relevant oscillation probabilities, and
illustrated with numerical simulations of realistic experimental setups.
Possible configurations where this method could be applied are the combination
of a super beam experiment with a beta beam or a neutrino factory, or a (low
energy) neutrino factory using a detector with muon and electron charge
identification.Comment: 13 pages, 3 figure
General bounds on non-standard neutrino interactions
We derive model-independent bounds on production and detection non-standard
neutrino interactions (NSI). We find that the constraints for NSI parameters
are around O(10^{-2}) to O(10^{-1}). Furthermore, we review and update the
constraints on matter NSI. We conclude that the bounds on production and
detection NSI are generally one order of magnitude stronger than their matter
counterparts.Comment: 18 pages, revtex4, 1 axodraw figure. Minor changes, matches published
versio
Loop bounds on non-standard neutrino interactions
We reconsider the bounds on non-standard neutrino interactions with matter
which can be derived by constraining the four-charged-lepton operators induced
at the loop level. We find that these bounds are model dependent. Naturalness
arguments can lead to much stronger constraints than those presented in
previous studies, while no completely model-independent bounds can be derived.
We will illustrate how large loop-contributions to four-charged-lepton
operators are induced within a particular model that realizes gauge invariant
non-standard interactions and discuss conditions to avoid these bounds. These
considerations mainly affect the constraint on the
non-standard coupling strength \eps_{e\mu}, which is lost. The only
model-independent constraints that can be derived are .
However, significant cancellations are required in order to saturate this
bound.Comment: Minor changes, version to be published in JHEP. 17 pages, 3 Axodraw
figures, REVTeX
Reactor Neutrino Experiments with a Large Liquid Scintillator Detector
We discuss several new ideas for reactor neutrino oscillation experiments
with a Large Liquid Scintillator Detector. We consider two different scenarios
for a measurement of the small mixing angle with a mobile
source: a nuclear-powered ship, such as a submarine or an
icebreaker, and a land-based scenario with a mobile reactor. The former setup
can achieve a sensitivity to at the 90%
confidence level, while the latter performs only slightly better than Double
Chooz. Furthermore, we study the precision that can be achieved for the solar
parameters, and , with a mobile reactor
and with a conventional power station. With the mobile reactor, a precision
slightly better than from current global fit data is possible, while with a
power reactor, the accuracy can be reduced to less than 1%. Such a precision is
crucial for testing theoretical models, e.g. quark-lepton complementarity.Comment: 18 pages, 3 figures, 2 tables, revised version, to appear in JHEP,
Fig. 1 extended, Formula added, minor changes, results unchange
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