705 research outputs found
Stability of three neutrino flavor conversion in supernovae
Neutrino-neutrino interactions can lead to collective flavor conversion in
the dense parts of a core collapse supernova. Growing instabilities that lead
to collective conversions have been studied intensely in the limit of
two-neutrino species and occur for inverted mass ordering in the case of a
perfectly spherical supernova. We examine two simple models of colliding and
intersecting neutrino beams and show, that for three neutrino species
instabilities exist also for normal mass ordering even in the case of a fully
symmetric system. Whereas the instability for inverted mass ordering is
associated with , the new instability we find for normal mass
ordering is associated with . As a consequence, the growth
rate of these new instabilities for normal ordering is smaller by about an
order of magnitude compared to the rates of the well studied case of inverted
ordering.Comment: 18 pages, 5 figures Minor update on the consistency of the formulae
and prefactors, actualized plot
IceCube Flavor Ratios with Identified Astrophysical Sources: Towards Improving New Physics Testability
Motivated by the discovery of the first high-energy astrophysical neutrino
source, the blazar TXS 0506+056, we revisit the IceCube flavor ratio analysis.
Assuming large statistics from identified blazars, collected in the forthcoming
years by the IceCube detector and its successor IceCube-Gen2, we demonstrate
that the constraints on several new physics scenarios in which the baseline
dependent terms in neutrino oscillation probabilities are not averaged, can be
improved. As a representative case, we consider pseudo-Dirac neutrinos while
neutrino decay is also discussed.Comment: 17 pages, 5 figure
Langsomfiltres effekt på drikkevands biostabilitet - Litteraturudredning:Udført for Københavns Energi
Neutrino flavor mixing breaks isotropy in the early universe
The neutrino field is commonly assumed to be isotropic and homogeneous in the
early universe. However, due to the large neutrino density, a small
perturbation of the isotropy of the neutrino field could potentially be
amplified by the non-linear flavor mixing caused by neutrino self-interactions.
We carry out the first numerical simulations of the neutrino flavor evolution
in a multi-angle anisotropic setting. Due to the computational challenges
involved, we adopt a simplified framework consisting of a homogeneous universe
with two angle bins -- left and right moving modes -- for neutrinos and
antineutrinos, together with an approximate form for the collision term which
goes beyond the commonly adopted damping approximation. By assuming a small
initial left-right asymmetry of , we convincingly
demonstrate that flavor evolution can be affected in both mass orderings, with
implications on the effective number of thermally excited neutrino species
(). Notably, the correction to is comparable to
higher order corrections from finite temperature QED effects in normal
ordering. In addition, by assuming an initial lepton asymmetry in the neutrino
sector of the same order as the baryon one [], we find
that the neutrino-antineutrino asymmetry grows by several orders of magnitude
for isotropic as well as anisotropic initial conditions. This work clearly
shows that it is imperative to critically revisit standard assumptions
concerning neutrino flavor mixing in the early universe, especially in the
light of possible implications on the cosmological observables.Comment: 44 pages, 10 figures. Updated with an improved linear stability
analysis. Accepted for publication in JCA
A Prismatic Analyser concept for Neutron Spectrometers
A development in modern neutron spectroscopy is to avoid the need of large
samples. We demonstrate how small samples together with the right choice of
analyser and detector components makes distance collimation an important
concept in crystal analyser spectrometers. We further show that this opens new
possibilities where neutrons with different energies are reflected by the same
analyser but counted in different detectors, thus improving both energy
resolution and total count rate compared to conventional spectrometers. The
technique can be combined with advanced focusing geometries and with
multiplexing instrument designs. We present a combination of simulations and
data with 3 energies from one analyser. The data was taken on a prototype
installed at PSI, Switzerland, and shows excellent agreement with the
predictions. Typical improvements will be 2 times finer resolution and a factor
1.9 in flux gain compared to a Rowland geometry or 3 times finer resolution and
a factor 3.2 in flux gain compared to a single flat analyser slab
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