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ABSTRACT: We point out that for sterile neutrinos of the eV mass scale with mixing
parameters suggested by the reactor neutrino anomaly, substantial flavor
transformation occurs in both \nu_e-\nu_s and \bar \nu_e-\bar \nu_s channels
near a supernova core where the electron-to-baryon ratio is \approx 1/3. We
show that the rate of heating by neutrino reactions in the shocked material is
significantly reduced for \sim 100 ms after the launch of the shock in
spherically symmetric models of 8.8 and 11.2 Msun supernovae. While the exact
consequences must be evaluated by incorporating \nu_e-\nu_s and \bar \nu_e-\bar
\nu_s conversion self-consistently in the models, our results suggest that such
flavor transformation would have important effects on the supernova explosion
mechanisms and possibly also on nucleosynthesis in the neutrino-heated ejecta.
We explore the sensitivity of our results to the mixing parameters and urge
that self-consistent supernova models be developed to constrain the allowed
parameter space.
05/2013;
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ABSTRACT: Many of the currently available equations of state for core-collapse
supernova simulations give large neutron star radii and do not provide large
enough neutron star masses, both of which are inconsistent with some recent
neutron star observations. In addition, one of the critical uncertainties in
the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully
explored by the currently available equations of state. In this article, we
construct two new equations of state which match recent neutron star
observations and provide more flexibility in studying the dependence on nuclear
matter properties. The equations of state are also provided in tabular form,
covering a wide range in density, temperature and asymmetry, suitable for
astrophysical simulations. These new equations of state are implemented into
our spherically symmetric core-collapse supernova model, which is based on
general relativistic radiation hydrodynamics with three-flavor Boltzmann
neutrino transport. The results are compared with commonly used equations of
state in supernova simulations of 15 and 40 solar mass progenitors. We do not
find any simple correlations between individual nuclear matter properties at
saturation and the outcome of these simulations. However, the new equations of
state lead to the most compact neutron stars among the relativistic mean-field
models which we considered. The new models also obey the previously observed
correlation between the time to black hole formation and the maximum mass of an
s=4 neutron star.
07/2012;
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ABSTRACT: By implementing widely-used equations of state (EOS) from Lattimer & Swesty
(LS) and H. Shen et al. (SHEN) in core-collapse supernova simulations, we
explore possible impacts of these EOS on the post-bounce dynamics prior to the
onset of neutrino-driven explosions. Our spherically symmetric (1D) and axially
symmetric (2D) models are based on neutrino radiation hydrodynamics including
spectral transport, which is solved by the isotropic diffusion source
approximation. We confirm that in 1D simulations neutrino-driven explosions
cannot be obtained for any of the employed EOS. Impacts of the EOS on the
post-bounce hydrodynamics are more clearly visible in 2D simulations. In 2D
models of a 15 M_sun progenitor using the LS EOS, the stalled bounce shock
expands to increasingly larger radii, which is not the case using the SHEN EOS.
Keeping in mind that the omission of the energy drain by heavy-lepton neutrinos
in the present scheme could facilitate explosions, we find that 2D models of an
11.2 M_sun progenitor produce neutrino-driven explosions for all the EOS under
investigation. Models using the LS EOS are slightly more energetic compared to
those with the SHEN EOS. The more efficient neutrino heating in the LS models
coincides with a higher electron antineutrino luminosity and a larger mass that
is enclosed within the gain region. The models based on the LS EOS also show a
more vigorous and aspherical downflow of accreting matter to the surface of the
protoneutron star (PNS). The accretion pattern is essential for the production
and strength of outgoing pressure waves, that can push in turn the shock to
larger radii and provide more favorable conditions for the explosion.
[abbreviated]
06/2012;
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Michael Wurm,
John F. Beacom,
Leonid B. Bezrukov,
Daniel Bick,
Johannes Blümer,
Sandhya Choubey,
Christian Ciemniak,
Davide D'Angelo,
Basudeb Dasgupta,
Amol Dighe, [......],
Valerij Sinev,
Christian Spiering,
Achim Stahl,
Felicitas Thorne,
Marc Tippmann,
Alessandra Tonazzo,
Wladyslaw H. Trzaska,
John D. Vergados,
Christopher Wiebusch,
Jürgen Winter
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ABSTRACT: 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.
Astroparticle Physics 04/2012; 35:685-732. · 3.22 Impact Factor
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ABSTRACT: We revisit our previous results on the matter suppression of self-induced
neutrino flavor conversions during a supernova (SN) accretion phase, performing
a linearized stability analysis of the neutrino equations of motion, in the
presence of realistic SN density profiles. In our previous numerical study, we
used a simplified model based on an isotropic neutrino emission with a single
typical energy. Here, we take into account realistic neutrino energy and angle
distributions. We find that multi-energy effects have a sub-leading impact in
the flavor stability of the SN neutrino fluxes with respect to our previous
single-energy results. Conversely, realistic forward-peaked neutrino angular
distributions would enhance the matter suppression of the self-induced
oscillations with respect to an isotropic neutrino emission. As a result, in
our models for iron-core SNe, collective flavor conversions have a negligible
impact on the characterization of the observable neutrino signal during the
accretion phase. Instead, for a low-mass O-Ne-Mg core SN model, with lower
matter density profile and less forward-peaked angular distributions,
collective conversions are possible also at early times.
03/2012;
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ABSTRACT: We explore heavy element nucleosynthesis in the explosion of massive stars
which are triggered by a quark-hadron phase transition during the early post
bounce phase of core-collapse supernovae. The present study is based on general
relativistic radiation hydrodynamics simulations with three-flavor Boltzmann
neutrino transport in spherical symmetry, which utilize a quark-hadron hybrid
equation of state based on the MIT bag model for strange quark matter. The
quark-hadron phase transition inside the stellar core forms a shock wave
propagating towards the surface of the proto-neutron star. The shock wave
results in an explosion and ejects neutron-rich matter which is piled up or
accreting on the proto-neutron star. Later, during the cooling phase, the
proto-neutron star develops a proton-rich neutrino-driven wind. We present a
detailed analysis of the nucleosynthesis outcome in both neutron-rich and
proton-rich ejecta and compare our integrated nucleosynthesis with observations
of metal poor stars.
12/2011;
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ABSTRACT: 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.
11/2011;
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ABSTRACT: We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle θ(13) is not very small.
Physical Review Letters 10/2011; 107(15):151101. · 7.37 Impact Factor
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ABSTRACT: We discuss three new equations of state (EOS) in core-collapse supernova
simulations. The new EOS are based on the nuclear statistical equilibrium model
of Hempel and Schaffner-Bielich (HS), which includes excluded volume effects
and relativistic mean-field (RMF) interactions. We consider the RMF
parameterizations TM1, TMA, and FSUgold. These EOS are implemented into our
spherically symmetric core-collapse supernova model, which is based on general
relativistic radiation hydrodynamics and three-flavor Boltzmann neutrino
transport. The results obtained for the new EOS are compared with the widely
used EOS of H. Shen et al. and Lattimer & Swesty. The systematic comparison
shows that the model description of inhomogeneous nuclear matter is as
important as the parameterization of the nuclear interactions for the supernova
dynamics and the neutrino signal. Furthermore, several new aspects of nuclear
physics are investigated: the HS EOS contains distributions of nuclei,
including nuclear shell effects. The appearance of light nuclei, e.g.,
deuterium and tritium is also explored, which can become as abundant as alphas
and free protons. In addition, we investigate the black hole formation in
failed core-collapse supernovae, which is mainly determined by the high-density
EOS. We find that temperature effects lead to a systematically faster collapse
for the non-relativistic LS EOS in comparison to the RMF EOS. We deduce a new
correlation for the time until black hole formation, which allows to determine
the maximum mass of proto-neutron stars, if the neutrino signal from such a
failed supernova would be measured in the future. This would give a constraint
for the nuclear EOS at finite entropy, complementary to observations of cold
neutron stars.
The Astrophysical Journal 08/2011; 748(1). · 6.02 Impact Factor
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ABSTRACT: The usual description of self-induced neutrino flavor conversions in core
collapse supernovae (SNe) is based on the dominance of the neutrino density
n_nu over the net electron density n_e. However, this condition is not met
during the post-bounce accretion phase, when the dense matter in a SN is piled
up above the neutrinosphere. As recently pointed-out, a dominant matter term in
the anisotropic SN environment would dephase the flavor evolution for neutrinos
traveling on different trajectories, challenging the occurrence of the
collective behavior in the dense neutrino gas. Using the results from recent
long term simulations of core-collapse SN explosions, based on three flavor
Boltzmann neutrino transport in spherical symmetry, we find that both the
situations of complete matter suppression (when n_e >> n_nu) and matter-induced
decoherence (when n_e \gtrsim n_nu) of flavor conversions are realized during
the accretion phase. The matter suppression at high densities prevents any
possible impact of the neutrino oscillations on the neutrino heating and hence
on the dynamics of the explosion. Furthermore, it changes the interpretation of
the Earth matter effect on the SN neutrino signal during the accretion phase,
allowing the possibility of the neutrino mass hierarchy discrimination at not
too small values of the leptonic mixing angle \theta_{13} (i.e.
\sin^2{\theta}_{13} \gtrsim 10^{-3}).
05/2011;
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ABSTRACT: The implications of a QCD phase transition at high temperatures and densities for core-collapse supernovae are discussed. For a strong first order phase transition to quark matter, various scenarios have been put forward in the literature. Here, detailed numerical simulations including neutrino transport are presented, where it is found that a second shock wave due to the QCD phase transition emerges shortly after bounce. It is demonstrated that such a supernova banging twice results in a second peak in the antineutrino spectrum. This second peak is clearly detectable in present neutrino detectors for a galactic supernova. Comment: 6 pages, 3 figures, invited talk given at the Yukawa International Program for Quark-Hadron Sciences: New Frontiers in QCD 2010, Kyoto, Japan, to be published in Progress of Theoretical Physics
09/2010;
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ABSTRACT: Predictions of the thermodynamic conditions for phase transitions at high baryon densities and large chemical potentials are currently uncertain and largely phenomenological. Neutrino observations of core-collapse supernovae can be used to constrain the situation. Recent simulations of stellar core collapse that include a description of quark matter predict a sharp burst of anti \nu_e several hundred milliseconds after the prompt \nu_e neutronization burst. We study the observational signatures of that anti \nu_e burst at current neutrino detectors - IceCube and Super-Kamiokande. For a Galactic core-collapse supernova, we find that signatures of the QCD phase transition can be detected, regardless of the neutrino oscillation scenario. The detection would constitute strong evidence of a phase transition in the stellar core, with implications for the equation of state at high matter density and the supernova explosion mechanism. Comment: 6 pages, 4 figures; matches published version (1 additional figure, added discussion of subsampling at IceCube). Accepted for publication in PRD
12/2009;
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ABSTRACT: The possible role of a first order QCD phase transition at nonvanishing quark chemical potential and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars, we use the NJL model with nonvanishing color superconducting pairing gaps, which describes the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We demonstrate that these two phase transitions can both be present in the core of neutron stars and that they lead to the appearance of a third family of solution for compact stars. In particular, a core of CFL quark matter can be present in stable compact star configurations when slightly adjusting the vacuum pressure to the onset of the chiral phase transition from the hadronic model to the NJL model. We show that a strong first order phase transition can have strong impact on the dynamics of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a second outgoing shock wave can be generated which leads to an explosion. The presence of the QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova. Comment: 5 pages, invited talk given at the 8th International Conference on Quark Confinement and the Hadron Spectrum, September 1-5, 2008, Mainz, Germany
03/2009;
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ABSTRACT: The implications of the formation of strange quark matter in neutron stars and in core-collapse supernovae is discussed with special emphasis on the possibility of having a strong first order QCD phase transition at high baryon densities. If strange quark matter is formed in core-collapse supernovae shortly after the bounce, it causes the launch of a second outgoing shock which is energetic enough to lead to a explosion. A signal for the formation of strange quark matter can be read off from the neutrino spectrum, as a second peak in antineutrinos is released when the second shock runs over the neutrinosphere. Comment: 10 pages, 8 figures, invited talk given at the international conference on strangeness in quark matter (SQM2008), Beijing, October 6-10, Beijing, China, version to appear in J. Phys. G
Journal of Physics G Nuclear and Particle Physics 02/2009; · 4.18 Impact Factor
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ABSTRACT: We discuss the formation of stellar mass black holes via protoneutron star (PNS) collapse. Such PNSs are modelled as central objects in general relativistic ID core collapse simulations with Boltzmann neutrino transport. In the absence of an earlier explosion, the PNS collapses eventually due to continued accretion of outer layers of a massive star onto the central object. We investigate the resulting conditions with respect to neutrino emission at the formation of a black hole.
Journal of Physics Conference Series 05/2007; 66(1):012043.
