7 research outputs found
Supernova neutrino halo and the suppression of self-induced flavor conversion
Neutrinos streaming from a supernova (SN) core occasionally scatter in the
envelope, producing a small "neutrino halo" with a much broader angle
distribution than the primary flux originating directly from the core. Cherry
et al. (2012) have recently pointed out that, during the accretion phase, the
halo actually dominates neutrino-neutrino refraction at distances exceeding
some 100 km. However, the multiangle matter effect (which increases if the
angle distribution is broader) still appears to suppress self-induced flavor
conversion during the accretion phase.Comment: related to our previous PRL 108 (2012) 061101 [arXiv:1109.3601]; v2
with appendix on analytic treatment of halo, matches the published versio
Suppression of Self-Induced Flavor Conversion in the Supernova Accretion Phase
Self-induced flavor conversions of supernova (SN) neutrinos can strongly
modify the flavor dependent fluxes. We perform a linearized flavor stability
analysis with accretion-phase matter profiles of a 15 M_sun spherically
symmetric model and corresponding neutrino fluxes. We use realistic energy and
angle distributions, the latter deviating strongly from quasi-isotropic
emission, thus accounting for both multi-angle and multi-energy effects. For
our matter and neutrino density profile we always find stable conditions:
flavor conversions are limited to the usual MSW effect. In this case one may
distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing
angle theta_13 is as large as suggested by recent experiments.Comment: 4 pages, 5 figures; minor edits, matches the version published in PR
Probing the neutrino mass hierarchy with the rise time of a supernova burst
The rise time of a Galactic supernova (SN) bar-nue lightcurve, observable at
a high-statistics experiment such as the IceCube Cherenkov detector, can
provide a diagnostic tool for the neutrino mass hierarchy at "large" 1-3
leptonic mixing angle theta_13. Thanks to the combination of matter suppression
of collective effects at early postbounce times on one hand and the presence of
the ordinary Mikheyev-Smirnov-Wolfenstein effect in the outer layers of the SN
on the other hand, a sufficiently fast rise time on O(100) ms scale is
indicative of an inverted mass hierarchy. We investigate results from an
extensive set of stellar core-collapse simulations, providing a first
exploration of the astrophysical robustness of these features. We find that for
all the models analyzed (sharing the same weak interaction microphysics) the
rise times for the same hierarchy are similar not only qualitatively, but also
quantitatively, with the signals for the two classes of hierarchies
significantly separated. We show via Monte Carlo simulations that the two cases
should be distinguishable at IceCube for SNe at a typical Galactic distance 99%
of the times. Finally, a preliminary survey seems to show that the faster rise
time for inverted hierarchy as compared to normal hierarchy is a qualitatively
robust feature predicted by several simulation groups. Since the viability of
this signature ultimately depends on the quantitative assessment of
theoretical/numerical uncertainties, our results motivate an extensive campaign
of comparison of different code predictions at early accretion times with
implementation of microphysics of comparable sophistication, including effects
such like nucleon recoils in weak interactions.Comment: 17 pages, 5 figures, unchanged but for minor reference update,
matches published versio
Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows
Motivated by recent hints for sterile neutrinos from the reactor anomaly, we
study active-sterile conversions in a three-flavor scenario (2 active + 1
sterile families) for three different representative times during the
neutrino-cooling evolution of the proto-neutron star born in an
electron-capture supernova. In our "early model" (0.5 s post bounce), the
nu_e-nu_s MSW effect driven by Delta m^2=2.35 eV^2 is dominated by ordinary
matter and leads to a complete nu_e-nu_s swap with little or no trace of
collective flavor oscillations. In our "intermediate" (2.9 s p.b.) and "late
models" (6.5 s p.b.), neutrinos themselves significantly modify the nu_e-nu_s
matter effect, and, in particular in the late model, nu-nu refraction strongly
reduces the matter effect, largely suppressing the overall nu_e-nu_s MSW
conversion. This phenomenon has not been reported in previous studies of
active-sterile supernova neutrino oscillations. We always include the feedback
effect on the electron fraction Y_e due to neutrino oscillations. In all
examples, Y_e is reduced and therefore the presence of sterile neutrinos can
affect the conditions for heavy-element formation in the supernova ejecta, even
if probably not enabling the r-process in the investigated outflows of an
electron-capture supernova. The impact of neutrino-neutrino refraction is
strong but complicated, leaving open the possibility that with a more complete
treatment, or for other supernova models, active-sterile neutrino oscillations
could generate conditions suitable for the r-process.Comment: 23 pages, including 14 figures and 2 tables (minor changes in the
text). Matches published version in JCA
The next-generation liquid-scintillator neutrino observatory LENA
We propose the liquid-scintillator detector LENA (Low Energy Neutrino
Astronomy) as a next-generation neutrino observatory on the scale of 50 kt. The
outstanding successes of the Borexino and KamLAND experiments demonstrate the
large potential of liquid-scintillator detectors in low-energy neutrino
physics. LENA's physics objectives comprise the observation of astrophysical
and terrestrial neutrino sources as well as the investigation of neutrino
oscillations. In the GeV energy range, the search for proton decay and
long-baseline neutrino oscillation experiments complement the low-energy
program. Based on the considerable expertise present in European and
international research groups, the technical design is sufficiently mature to
allow for an early start of detector realization.Comment: Whitepaper for the LENA low-energy neutrino detector, 67 pages, 32
figure