49 research outputs found
Multi-azimuthal-angle instability for different supernova neutrino fluxes
It has been recently discovered that removing the axial symmetry in the
"multi-angle effects" associated with the neutrino-neutrino interactions for
supernova (SN) neutrinos, a new multi-azimuthal-angle (MAA) instability would
trigger flavor conversions in addition to the ones caused by the bimodal and
multi-zenith-angle (MZA) instabilities. We investigate the dependence of the
MAA instability on the original SN neutrino fluxes, performing a stability
analysis of the linearized neutrino equations of motion. We compare these
results with the numerical evolution of the SN neutrino non-linear equations,
looking at a local solution along a specific line of sight, under the
assumption that the transverse variations of the global solution are small. We
also assume that self-induced conversions are not suppressed by large matter
effects. We show that the pattern of the spectral crossings (energies where
F_{\nu_e} = F_{\nu_x}, and F_{\bar\nu_e} = F_{\bar\nu_x}) is crucial in
determining the impact of MAA effects on the flavor evolution. For neutrino
spectra with a strong excess of \nu_e over \bar\nu_e, presenting only a
single-crossing, MAA instabilities would trigger new flavor conversions in
normal mass hierarchy. In our simplified flavor evolution scheme, these would
lead to spectral swaps and splits analogous to what produced in inverted
hierarchy by the bimodal instability. Conversely, in the presence of spectra
with a moderate flavor hierarchy, having multiple crossing energies, MZA
effects would produce a sizable delay in the onset of the flavor conversions,
inhibiting the growth of the MAA instability. In this case the splitting
features for the oscillated spectra in both the mass hierarchies are the ones
induced by the only bimodal and MZA effects.Comment: (v2: 13 pages, 9 eps figures. Revised version. Accepted for
publication in PRD. Major changes: Stability analysis added. Results
unchanged
Diffuse neutrinos from extragalactic supernova remnants: Dominating the 100 TeV IceCube flux
IceCube has measured a diffuse astrophysical flux of TeV-PeV neutrinos. The
most plausible sources are unique high energy cosmic ray accelerators like
hypernova remnants (HNRs) and remnants from gamma ray bursts in star-burst
galaxies, which can produce primary cosmic rays with the required energies and
abundance. In this case, however, ordinary supernova remnants (SNRs), which are
far more abundant than HNRs, produce a comparable or larger neutrino flux in
the ranges up to 100-150 TeV energies, implying a spectral break in the IceCube
signal around these energies. The SNRs contribution in the diffuse flux up to
these hundred TeV energies provides a natural baseline and then constrains the
expected PeV flux.Comment: 12 pages, 2 figures, minor changes, comments and references added,
matches the published versio
Testing Lorentz invariance with neutrino bursts from supernova neutronization
Quantum-gravity (QG) effects might generate Lorentz invariance violation by
the interaction of energetic particles with the foamy structure of the
space-time. As a consequence, particles may not travel at the universal speed
of light. We propose to constrain Lorentz invariance violation for energetic
neutrinos exploiting the neutronization burst from the next galactic
supernova (SN). This prompt signal is expected to produce a sharp peak in the
SN light curve with a duration of ms. However presence of
energy-dependent Lorentz invariance violation would significantly spread out
the time structure of this signal. We find that the detection the SN
burst from a typical galactic explosion at kpc in a Mton-class water
Cerenkov detector, would be sensitive to a quantum-gravity mass scale GeV ( GeV) for the linear (quadratic) energy
dependence of Lorentz invariance violation. These limits are rather independent
of the neutrino mass hierarchy and whether the neutrino velocity is super or
subluminal.Comment: 4 pages, 3 figures, Revised version. Minor changes. Matches published
versio
Collective neutrino flavor conversion: Recent developments
Neutrino flavor evolution in core-collapse supernovae, neutron-star mergers,
or the early universe is dominated by neutrino-neutrino refraction, often
spawning "self-induced flavor conversion", i.e., shuffling of flavor among
momentum modes. This effect is driven by collective run-away modes of the
coupled "flavor oscillators" and can spontaneously break the initial symmetries
such as axial symmetry, homogeneity, isotropy, and even stationarity. Moreover,
the growth rates of unstable modes can be of the order of the neutrino-neutrino
interaction energy instead of the much smaller vacuum oscillation frequency:
self-induced flavor conversion does not always require neutrino masses. We
illustrate these newly found phenomena in terms of simple toy models. What
happens in realistic astrophysical settings is up to speculation at present.Comment: 16 pages, 3 figure
Self-induced neutrino flavor conversion without flavor mixing
Neutrino-neutrino refraction in dense media can cause self-induced flavor
conversion triggered by collective run-away modes of the interacting flavor
oscillators. The growth rates were usually found to be of order a typical
vacuum oscillation frequency . However, even in the simple case
of a beam interacting with an opposite-moving beam, and
allowing for spatial inhomogeneities, the growth rate of the fastest-growing
Fourier mode is of order , a typical
-- interaction energy. This growth rate is much larger than the
vacuum oscillation frequency and gives rise to flavor conversion on a much
shorter time scale. This phenomenon of "fast flavor conversion" occurs even for
vanishing and thus does not depend on energy, but only on the
angle distributions. Moreover, it does not require neutrinos to mix or to have
masses, except perhaps for providing seed disturbances. We also construct a
simple homogeneous example consisting of intersecting beams and study a
schematic supernova model proposed by Ray Sawyer, where and
emerge with different zenith-angle distributions, the key ingredient for fast
flavor conversion. What happens in realistic astrophysical scenarios remains to
be understood.Comment: 17 pages, 6 figures. Minor changes and updated references. Content
matches published versio
Supernova deleptonization asymmetry: Impact on self-induced flavor conversion
During the accretion phase of a core-collapse supernova (SN), the
deleptonization flux has recently been found to develop a global dipole pattern
(LESA---Lepton Emission Self-sustained Asymmetry). The minus
flux essentially vanishes in one direction, potentially
facilitating self-induced flavor conversion. On the other hand, below the
stalled shock wave, self-induced flavor conversion is typically suppressed by
multi-angle matter effects, preventing any impact of flavor conversion on SN
explosion dynamics. In a schematic model of SN neutrino fluxes, we study the
impact of modified - flux asymmetries on collective flavor
conversion. In the parameter space consisting of matter density and effective
neutrino density, the region of instability with regard to self-induced flavor
conversion is much larger for a vanishing lepton number flux, yet this
modification does not intersect a realistic SN profile. Therefore, it appears
that, even in the presence of LESA, self-induced flavor conversion remains
suppressed below the shock front.Comment: 14 pages, 6 figures; v2: significant change in presentation, results
and conclusion unchanged, appendix adde