215 research outputs found
The diffuse neutrino flux from supernovae: upper limit on the electron neutrino component from the non-observation of antineutrinos at SuperKamiokande
I derive an upper bound on the electron neutrino component of the diffuse
supernova neutrino flux from the constraint on the antineutrino component at
SuperKamiokande. The connection between antineutrino and neutrino channels is
due to the similarity of the muon and tau neutrino and antineutrino fluxes
produced in a supernova, and to the conversion of these species into electron
neutrinos and antineutrinos inside the star. The limit on the electron neutrino
flux is 5.5 cm^-2 s^-1 above 19.3 MeV of neutrino energy, and is stronger than
the direct limit from Mont Blanc by three orders of magnitude. It represents
the minimal sensitivity required at future direct searches, and is intriguingly
close to the reach of the Sudbury Neutrino Observatory (SNO) and of the ICARUS
experiment. The electron neutrino flux will have a lower bound if the electron
antineutrino flux is measured. Indicatively, the first can be smaller than the
second at most by a factor of 2-3 depending on the details of the neutrino
spectra at production.Comment: LaTeX, 5 pages, 1 figure. Paper is modified in the presentation (Fig.
1 was replaced with a different plot and Table 1 was expanded), with
unchanged results. References added and correcte
Signatures of supernova neutrino oscillations in the Earth mantle and core
The Earth matter effects on supernova (SN) neutrinos can be identified at a
single detector through peaks in the Fourier transform of their ``inverse
energy'' spectrum. The positions of these peaks are independent of the SN
models and therefore the peaks can be used as a robust signature of the Earth
matter effects, which in turn can distinguish between different neutrino mixing
scenarios. Whereas only one genuine peak is observable when the neutrinos
traverse only the Earth mantle, traversing also the core gives rise to multiple
peaks. We calculate the strengths and positions of these peaks analytically and
explore their features at a large scintillation detector as well as at a
megaton water Cherenkov detector through Monte Carlo simulations. We propose a
simple algorithm to identify the peaks in the actual data and quantify the
chances of a peak identification as a function of the location of the SN in the
sky.Comment: 17 pages, 9 figure
A test of tau neutrino interactions with atmospheric neutrinos and K2K
The presence of a tau component in the flux of atmospheric neutrinos inside
the Earth, due to flavor oscillations, makes these neutrinos a valuable probe
of interactions of the tau neutrino with matter. We study -- analytically and
numerically -- the effects of nonstandard interactions in the nu_e-nu_tau
sector on atmospheric neutrino oscillations, and calculate the bounds on the
exotic couplings that follow from combining the atmospheric neutrino and K2K
data. We find very good agreement between numerical results and analytical
predictions derived from the underlying oscillation physics. While improving on
existing accelerator bounds, our bounds still allow couplings of the size
comparable to the standard weak interaction. The inclusion of new interactions
expands the allowed region of the vacuum oscillation parameters towards smaller
mixing angles, 0.2 ~< sin^2 theta_{23} ~< 0.7, and slightly larger mass squared
splitting, 1.5 * 10^{-3} eV^2 ~< |\Delta m^2_{23}| ~< 4.0 * 10^{-3} eV^2,
compared to the standard case. The impact of the K2K data on all these results
is significant; further important tests of the nu_e-nu_tau exotic couplings
will come from neutrino beams experiments such as MINOS and long baseline
projects.Comment: 8 figures, some typos corrected, minor editing in the reference
Neutrino oscillation signatures of oxygen-neon-magnesium supernovae
We discuss the flavor conversion of neutrinos from core collapse supernovae
that have oxygen-neon-magnesium (ONeMg) cores. Using the numerically calculated
evolution of the star up to 650 ms post bounce, we find that, for the normal
mass hierarchy, the electron neutrino flux in a detector shows signatures of
two typical features of an ONeMg-core supernova: a sharp step in the density
profile at the base of the He shell and a faster shock wave propagation
compared to iron core supernovae. Before the shock hits the density step (t ~
150 ms), the survival probability of electron neutrinos is about 0.68, in
contrast to values of 0.32 or less for an iron core supernova. The passage of
the shock through the step and its subsequent propagation cause a decrease of
the survival probability and a decrease of the amplitude of oscillations in the
Earth, reflecting the transition to a more adiabatic propagation inside the
star. These changes affect the lower energy neutrinos first; they are faster
and more sizable for larger theta_13. They are unique of ONeMg-core supernovae,
and give the possibility to test the speed of the shock wave. The time
modulation of the Earth effect and its negative sign at the neutronization peak
are the most robust signatures in a detector.Comment: 14 pages, 10 figures (16 figure files). Text and graphics added for
illustration and clarification; Results unchanged. Version accepted for
publication in Physical Review
AI-based Ecological Monitoring of Handwriting to Early Detect Cognitive Decline
The early detection of Mild Cognitive Impairment (MCI) is fundamental to initiate treatments for delaying the onset of dementia. Currently, the Mini Mental State Examination (MMSE) is one of the most common clinical scales used by geriatricians to assess cognitive function. A deviation of 1 to 3 points from the maximum score (30) is considered as sign of relevant cognitive decline. However, objective and affordable tools are needed to complement the screening process. The quantitative analysis of handwriting represents a suitable solution, as the gesture is significantly impaired in MCI subjects in terms of time, speed, fluency and applied pressure. This works presents the development and testing of classification models able to separate subjects at risk of cognitive decline (MMSE <= 28) from controls (MMSE > 28), starting from free-content handwriting data acquired with a smart ink pen, used on paper, from which 36 indicators were computed. Data were collected in 2 phases. The former involved 45 subjects and served for models training. In the latter, data were acquired from 23 subjects in a domestic longitudinal framework and were partially used for model refinement, but mainly for testing. Three different algorithms were tried (support vector machine, random forest and Catboost) The best test performances on the longitudinal data were obtained by a Catboost classifier, achieving accuracy 93.33%, precision 88.89%, recall 100% and f1 score 94.12%. The results support the use of computerized handwriting analysis as screening tool for cognitive decline detection
Cosmic Strings as Emitters of Extremely High Energy Neutrinos
We study massive particle radiation from cosmic string kinks, and its
observability in extremely high energy neutrinos. In particular, we consider
the emission of moduli --- weakly coupled scalar particles predicted in
supersymmetric theories --- from the kinks of cosmic string loops. Since kinks
move at the speed of light on strings, moduli are emitted with large Lorentz
factors, and eventually decay into many pions and neutrinos via hadronic
cascades. The produced neutrino flux has energy ,
and is affected by oscillations and absorption (resonant and non-resonant). It
is observable at upcoming neutrino telescopes such as JEM-EUSO, and the radio
telescopes LOFAR and SKA, for a range of values of the string tension, and of
the mass and coupling constant of the moduli.Comment: 13 pages, 2 figure
Diffuse supernova neutrinos: oscillation effects, stellar cooling and progenitor mass dependence
We estimate the diffuse supernova neutrino background (DSNB) using the recent
progenitor-dependent, long-term supernova simulations from the Basel group and
including neutrino oscillations at several post-bounce times. Assuming
multi-angle matter suppression of collective effects during the accretion
phase, we find that oscillation effects are dominated by the matter-driven MSW
resonances, while neutrino-neutrino collective effects contribute at the 5-10%
level. The impact of the neutrino mass hierarchy, of the time-dependent
neutrino spectra and of the diverse progenitor star population is 10% or less,
small compared to the uncertainty of at least 25% of the normalization of the
supernova rate. Therefore, assuming that the sign of the neutrino mass
hierarchy will be determined within the next decade, the future detection of
the DSNB will deliver approximate information on the MSW-oscillated neutrino
spectra. With a reliable model for neutrino emission, its detection will be a
powerful instrument to provide complementary information on the star formation
rate and for learning about stellar physics.Comment: 19 pages, including 4 figures and 1 table. Clarifying paragraphs
added; results unchanged. Matches published version in JCA
Neutrino flavor conversion in a neutrino background: single- versus multi-particle description
In the early Universe, or near a supernova core, neutrino flavor evolution
may be affected by coherent neutrino-neutrino scattering. We develop a
microscopic picture of this phenomenon. We show that coherent scattering does
not lead to the formation of entangled states in the neutrino ensemble and
therefore the evolution of the system can always be described by a set of
one-particle equations. We also show that the previously accepted formalism
overcounts the neutrino interaction energy; the correct one-particle evolution
equations for both active-active and active-sterile oscillations contain
additional terms. These additional terms modify the index of refraction of the
neutrino medium, but have no effect on oscillation physics.Comment: 12 pages, 3 figures, minor typos correcte
Do many-particle neutrino interactions cause a novel coherent effect?
We investigate whether coherent flavor conversion of neutrinos in a neutrino
background is substantially modified by many-body effects, with respect to the
conventional one-particle effective description. We study the evolution of a
system of interacting neutrino plane waves in a box. Using its equivalence to a
system of spins, we determine the character of its behavior completely
analytically. We find that, if the neutrinos are initially in flavor
eigenstates, no coherent flavor conversion is realized, in agreement with the
effective one-particle description. This result does not depend on the size of
the neutrino wavepackets and therefore has a general character. The validity of
the several important applications of the one-particle formalism is thus
confirmed.Comment: 25 pages, 1 figur
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