73 research outputs found
Two modes of searching for new neutrino interactions at MINOS
The SuperKamiokande atmospheric neutrino measurements leave substantial room
for nonstandard interactions (NSI) of neutrinos with matter in the nu_e- nu_tau
sector. Large values of the NSI couplings are accommodated if the vacuum
oscillation parameters are changed from their standard values. Short and medium
baseline neutrino beams can break this degeneracy by measuring the true vacuum
oscillation parameters with the muon neutrino disappearance mode, for which the
matter effects are negligible or subdominant. These experiments can also search
for the nu_e-nu_tau flavor changing effects directly, by looking for
nu_mu->nu_e conversion caused by the intervening matter. We discuss both of
these methods for the case of MINOS. We find that, while the present MINOS data
on nu_mu disappearance induce only minor changes on the constraints on the NSI
parameters, the situation will improve markedly with the planned increase of
the statistics by an order of magnitude. In that case, the precision will be
enough to distinguish certain presently allowed NSI scenarios from the no-NSI
case. NSI per quark of about 10% the size of the standard weak interaction
could give a nu_mu - nu_e conversion probability of the order ~ 10^{-2},
measurable by MINOS in the same high statistics scenario. In this nu_mu - nu_e
channel, the small effects of NSI could be comparable or larger than the vacuum
contribution of the small angle theta_{13}. The expected theta_{13} bound at
MINOS should be more properly interpreted as a bound in the theta_{13}-NSI
parameter space.Comment: 10 pages, 3 figures; noticed typos corrected, results unchange
High Energy Neutrinos from the Tidal Disruption of Stars
We study the production of high energy neutrinos in jets from the tidal
disruption of stars by supermassive black holes. The diffuse neutrino flux
expected from these tidal disruption events (TDEs) is calculated both
analytically and numerically, taking account the dependence of the rate of TDEs
on the redshift and black hole mass. We find that ~10% of the observed diffuse
flux at IceCube at an energy of about 1 PeV can come from TDEs if the
characteristics of known jetted tidal disruption events are assumed to apply to
the whole population of these sources. If, however, plausible scalings of the
jet Lorentz factor or variability timescale with the black hole mass are taken
into account, the contribution of the lowest mass black holes to the neutrino
flux is enhanced. In this case, TDEs can account for most of the neutrino flux
detected at IceCube, describing both the neutrino flux normalization and
spectral shape with moderate baryonic loadings. While the uncertainties on our
assumptions are large, a possible signature of TDEs as the origin of the
IceCube signal is the transition of the flux flavor composition from a pion
beam to a muon damped source at the highest energies, which will also result in
a suppression of Glashow resonance events.Comment: LaTeX, 30 pages, 6 figures. Added illustration of a case with
luminosity scaling, and an appendix on predicted X-ray flux. Figures added.
Conclusions unchanged. Version accepted in Phys. Rev.
Testing neutrino spectra formation in collapsing stars with the diffuse supernova neutrino flux
I address the question of what can be learned from the observation of the
diffuse supernova neutrino flux in the precision phase, at next generation
detectors of Megaton scale. An analytical study of the spectrum of the diffuse
flux shows that, above realistic detection thresholds of 10 MeV or higher, the
spectrum essentially reflects the exponential-times-polynomial structure of the
original neutrino spectrum at the emission point. There is only a weak (tens of
per cent) dependence on the power \beta describing the growth of the supernova
rate with the redshift. Different original neutrino spectra correspond to large
differences in the observed spectrum of events at a water Cerenkov detector:
for typical supernova rates, the ratio of the numbers of events in the first
and second energy bins (of 5 MeV width) varies in the interval 1.5 - 4.3 for
pure water (energy threshold 18 MeV) and in the range 1 - 2.5 for water with
Gadolinium (10 MeV threshold). In the first case discrimination would be
difficult due to the large errors associated with background. With Gadolinium,
instead, the reduction of the total error down to 10-20 % level would allow
spectral sensitivity, with a dramatic improvement of precision with respect to
the SN1987A data. Even in this latter case, for typical neutrino luminosity the
dependence on \beta is below sensitivity, so that it can be safely neglected in
data analysis.Comment: LaTeX, 10 pages, 5 figures; details added to fig. 5 and related text,
minor modifications to the text, references added. Version in press in
Phys.Rev.D
Diffuse neutrino flux from failed supernovae
I study the diffuse flux of electron antineutrinos from stellar collapses
with direct black hole formation (failed supernovae). This flux is more
energetic than that from successful supernovae, and therefore it might
contribute substantially to the total diffuse flux above realistic detection
thresholds. The total flux might be considerably higher than previously
thought, and approach the sensitivity of SuperKamiokande. For more conservative
values of the parameters, the flux from failed supernovae dominates for
antineutrino energies above 30-45 MeV, with potential to give an observable
spectral distortion at Megaton detectors.Comment: PDFLaTeX, 4 pages, 3 figures. New version has improved text and
graphics, references added. Results unchange
Solar neutrinos as probes of neutrino-matter interactions
Data from solar neutrino and KamLAND experiments have led to a discovery of
nonzero neutrino masses. Here we investigate what these data can tell us about
neutrino interactions with matter, including the poorly constrained
flavor-changing nu_e-nu_tau interactions. We give examples of the interaction
parameters that are excluded by the solar/KamLAND data and are beyond the reach
of other experiments. We also demonstrate that flavor-changing interactions, at
the allowed level, may profoundly modify the conversion probability for
neutrinos of energy <~ 6 MeV and the values of the mass parameter inferred from
the data. The implications for future experiments are discussed.Comment: 6 pages, 3 figure
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