224 research outputs found
The minimum width condition for neutrino conversion in matter
We find that for small vacuum mixing angle and low energies () the width of matter, , needed to have conversion probability
should be larger than : . Here is the Fermi constant, is the
total energy squared in the center of mass and is the mass of the
boson. The absolute minimum is realized for oscillations in a
uniform medium with resonance density. For all the other density distributions
(monotonically varying density, castle wall profile, etc.) the required width
is larger than . The width depends on , and for
-resonance channels at we get that is 20 times
smaller than the low energy value. We apply the minimum width condition, , to high energy neutrinos in matter as well as in neutrino background.
Using this condition, we conclude that the matter effect is negligible for
neutrinos propagating in AGN and GRBs environments. Significant conversion can
be expected for neutrinos crossing dark matter halos of clusters of galaxies
and for neutrinos produced by cosmologically distant sources and propagating in
the universe.Comment: 35 pages, latex, 5 figures, structure of the paper is slightly
changed, typos 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
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