712 research outputs found
Supernova neutrinos: Strong coupling effects of weak interactions
In core-collapse supernovae, neutrinos and antineutrinos are initially
subject to significant self-interactions induced by weak neutral currents,
which may induce strong-coupling effects on the flavor evolution (collective
transitions). The interpretation of the effects is simplified when self-induced
collective transitions are decoupled from ordinary matter oscillations, as for
the matter density profile that we discuss. In this case, approximate
analytical tools can be used (pendulum analogy, swap of energy spectra). For
inverted neutrino mass hierarchy, the sequence of effects involves:
synchronization, bipolar oscillations, and spectral split. Our simulations
shows that the main features of these regimes are not altered when passing from
simplified (angle-averaged) treatments to full, multi-angle numerical
experiments.Comment: Proceedings of NO-VE 2008, IV International Workshop on "Neutrino
Oscillations in Venice" (Venice, Italy, April 15-18, 2008), edited by M.
Baldo Ceolin (University of Padova publication, Papergraf Editions, Padova,
Italy, 2008), pages 233-24
Earth matter effects in supernova neutrinos: Optimal detector locations
A model-independent experimental signature for flavor oscillations in the
neutrino signal from the next Galactic supernova (SN) would be the observation
of Earth matter effects. We calculate the probability for observing a Galactic
SN shadowed by the Earth as a function of the detector's geographic latitude.
This probability depends only mildly on details of the Galactic SN
distribution. A location at the North Pole would be optimal with a shadowing
probability of about 60%, but a far-northern location such as Pyhasalmi in
Finland, the proposed site for a large-volume scintillator detector, is almost
equivalent (58%). We also consider several pairs of detector locations and
calculate the probability that only one of them is shadowed, allowing a
comparison between a shadowed and a direct signal. For the South Pole combined
with Kamioka this probability is almost 75%, for the South Pole combined with
Pyhasalmi it is almost 90%. One particular scenario consists of a large-volume
scintillator detector located in Pyhasalmi to measure the geo-neutrino flux in
a continental location and another such detector in Hawaii to measure it in an
oceanic location. The probability that only one of them is shadowed exceeds 50%
whereas the probability that at least one is shadowed is about 80%. We provide
an online tool to calculate different shadowing probabilities for the one- and
two-detector cases.Comment: v2: 17 pages, 6 eps figures. Typos removed, matches the published
version. Online tool to calculate the Earth shadowing probabilities available
at http://www.mppmu.mpg.de/supernova/shadowing . High-resolution color
version of fig_2a and fig_2b available at
http://www.mppmu.mpg.de/supernova/shadowing/ma
Probing supernova shock waves and neutrino flavor transitions in next-generation water-Cherenkov detectors
Several current projects aim at building a large water-Cherenkov detector,
with a fiducial volume about 20 times larger than in the current
Super-Kamiokande experiment. These projects include the Underground nucleon
decay and Neutrino Observatory (UNO) in the Henderson Mine (Colorado), the
Hyper-Kamiokande (HK) detector in the Tochibora Mine (Japan), and the MEgaton
class PHYSics (MEMPHYS) detector in the Frejus site (Europe). We study the
physics potential of a reference next-generation detector (0.4 Mton of fiducial
mass) in providing information on supernova neutrino flavor transitions with
unprecedented statistics. After discussing the ingredients of our calculations,
we compute neutrino event rates from inverse beta decay (), elastic scattering on electrons, and scattering on oxygen, with emphasis on
their time spectra, which may encode combined information on neutrino
oscillation parameters and on supernova forward (and possibly reverse) shock
waves. In particular, we show that an appropriate ratio of low-to-high energy
events can faithfully monitor the time evolution of the neutrino crossing
probability along the shock-wave profile. We also discuss some background
issues related to the detection of supernova relic neutrinos, with and without
the addition of gadolinium.Comment: Revised version (27 pages, 13 eps figures), to appear in JCAP.
Includes revised numerical estimates and figures. In particular: calculations
of inverse beta decay event rates improved by using the differential cross
section by Vissani and Strumia (astro-ph/0302055); supernova relic neutrino
flux calculations updated by using recent GALEX Mission data
(astro-ph/0411424) on the star formation rate (SFR). References added.
Conclusions unchange
Analysis of energy- and time-dependence of supernova shock effects on neutrino crossing probabilities
It has recently been realized that supernova neutrino signals may be affected
by shock propagation over a time interval of a few seconds after bounce. In the
standard three-neutrino oscillation scenario, such effects crucially depend on
the neutrino level crossing probability P_H in the 1-3 sector. By using a
simplified parametrization of the time-dependent supernova radial density
profile, we explicitly show that simple analytical expressions for P_H
accurately reproduce the phase-averaged results of numerical calculations in
the relevant parameter space. Such expressions are then used to study the
structure of P_H as a function of energy and time, with particular attention to
cases involving multiple crossing along the shock profile. Illustrative
applications are given in terms of positron spectra generated by supernova
electron antineutrinos through inverse beta decay.Comment: Major changes both in the text and in the figures in order to include
the effect of a step-like shock front density profile; final version to
appear in Physical Review
Axion hot dark matter bounds
We derive cosmological limits on two-component hot dark matter consisting of
neutrinos and axions. We restrict the large-scale structure data to the safely
linear regime, excluding the Lyman-alpha forest. We derive Bayesian credible
regions in the two-parameter space consisting of m_a and sum(m_nu).
Marginalizing over sum(m_nu) provides m_a<1.02 eV (95% CL). In the absence of
axions the same data and methods give sum(m_nu)< 0.63 eV (95% CL).Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs
(18-21 June 2008, DESY
Signatures of axion-like particles in the spectra of TeV gamma-ray sources
One interpretation of the unexplained signature observed in the PVLAS
experiment invokes a new axion-like particle (ALP) with a two-photon vertex,
allowing for photon-ALP oscillations in the presence of magnetic fields. In the
range of masses and couplings suggested by PVLAS, the same effect would lead to
a peculiar dimming of high-energy photon sources. For typical parameters of the
turbulent magnetic field in the galaxy, the effect sets in at E_gamma >~ 10
TeV, providing an ALP signature in the spectra of TeV gamma sources that can be
probed with Cherenkov telescopes. A dedicated search will be strongly motivated
if the ongoing photon regeneration experiments confirm the PVLAS particle
interpretation.Comment: 8 pages, 1 eps figure; typos corrected, matches published versio
Conversion of TeV photons in realistic extragalactic magnetic field
13th Patras Workshop on Axions, WIMPs and WISPs, Patras 2017, Thessaloniki, Greece, 15 May 2017 - 19 May 2017; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC, (2018). doi:10.3204/DESY-PROC-2017-0
Stochastic conversions of TeV photons into axion-like particles in extragalactic magnetic fields
Very-high energy photons emitted by distant cosmic sources are absorbed on
the extragalactic background light (EBL) during their propagation. This effect
can be characterized in terms of a photon transfer function at Earth. The
presence of extragalactic magnetic fields could also induce conversions between
very high-energy photons and hypothetical axion-like particles (ALPs). The
turbulent structure of the extragalactic magnetic fields would produce a
stochastic behaviour in these conversions, leading to a statistical
distribution of the photon transfer functions for the different realizations of
the random magnetic fields. To characterize this effect, we derive new
equations to calculate the mean and the variance of this distribution. We find
that, in presence of ALP conversions, the photon transfer functions on
different lines of sight could have relevant deviations with respect to the
mean value, producing both an enhancement or a suppression in the observable
photon flux with respect to the expectations with only absorption. As a
consequence, the most striking signature of the mixing with ALPs would be a
reconstructed EBL density from TeV photon observations which appears to vary
over different directions of the sky: consistent with standard expectations in
some regions, but inconsistent in others.Comment: v2: 22 pages, 5 eps figures. Minor changes. A reference added.
Matches the version published on JCA
Light sterile neutrino production in the early universe with dynamical neutrino asymmetries
Light sterile neutrinos mixing with the active ones have been recently
proposed to solve different anomalies observed in short-baseline oscillation
experiments. These neutrinos can also be produced by oscillations of the active
neutrinos in the early universe, leaving possible traces on different
cosmological observables. Here we perform an updated study of the neutrino
kinetic equations in (3+1) and (2+1) oscillation schemes, dynamically evolving
primordial asymmetries of active neutrinos and taking into account for the
first time CP-violation effects. In the absence of neutrino asymmetries,
eV-mass scale sterile neutrinos would be completely thermalized creating a
tension with respect to the CMB, LSS and BBN data. In the past literature,
active neutrino asymmetries have been invoked as a way to inhibit the sterile
neutrino production via the in-medium suppression of the sterile-active mixing
angle. However, neutrino asymmetries also permit a resonant sterile neutrino
production. We find that if the active species have equal asymmetries L, a
value |L|=10^{-3} is required to start suppressing the resonant sterile
production, roughly an order of magnitude larger than what previously expected.
When active species have opposite asymmetries the sterile abundance is further
enhanced, requiring an even larger |L|\simeq 10^{-2} to start suppressing their
production. In the latter case, CP-violation (naturally expected) further
exacerbates the phenomenon. Some consequences for cosmological observables are
briefly discussed: for example, it is likely that moderate suppressions of the
sterile species production are associated with significant spectral distortions
of the active neutrino species, with potentially interesting phenomenological
consequences especially for BBN.Comment: (v2: 22 pages, 10 eps figures. Revised version. Typos removed,
reference updated. Matches the version published on PRD.
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