7,184 research outputs found
Long-term evolution of massive star explosions
We examine simulations of core-collapse supernovae in spherical symmetry. Our
model is based on general relativistic radiation hydrodynamics with
three-flavor Boltzmann neutrino transport. We discuss the different supernova
phases, including the long-term evolution up to 20 seconds after the onset of
explosion during which the neutrino fluxes and mean energies decrease
continuously. In addition, the spectra of all flavors become increasingly
similar, indicating the change from charged- to neutral-current dominance.
Furthermore, it has been shown recently by several groups independently, based
on sophisticated supernova models, that collective neutrino flavor oscillations
are suppressed during the early mass-accretion dominated post-bounce evolution.
Here we focus on the possibility of collective flavor flips between electron
and non-electron flavors during the later, on the order of seconds, evolution
after the onset of an explosion with possible application for the
nucleosynthesis of heavy elements.Comment: 12 pages, 7 figures, conference proceeding, HANSE 2011 worksho
Core-collapse supernova explosions triggered by a quark-hadron phase transition during the early post-bounce phase
We explore explosions of massive stars, which are triggered via the
quark-hadron phase transition during the early post bounce phase of
core-collapse supernovae. We construct a quark equation of state, based on the
bag model for strange quark matter. The transition between the hadronic and the
quark phases is constructed applying Gibbs conditions. The resulting
quark-hadron hybrid equations of state are used in core-collapse supernova
simulations, based on general relativistic radiation hydrodynamics and three
flavor Boltzmann neutrino transport in spherical symmetry. The formation of a
mixed phase reduces the adiabatic index, which induces the gravitational
collapse of the central protoneutron star. The collapse halts in the pure quark
phase, where the adiabatic index increases. A strong accretion shock forms,
which propagates towards the protoneutron star surface. Due to the density
decrease of several orders of magnitude, the accretion shock turns into a
dynamic shock with matter outflow. This moment defines the onset of the
explosion in supernova models that allow for a quark-hadron phase transition,
where otherwise no explosions could be obtained. The shock propagation across
the neutrinospheres releases a burst of neutrinos. This serves as a strong
observable identification for the structural reconfiguration of the stellar
core. The ejected matter expands on a short timescale and remains neutron-rich.
These conditions might be suitable for the production of heavy elements via the
r-process. The neutron-rich material is followed by proton-rich neutrino-driven
ejecta in the later cooling phase of the protoneutron star where the vp-process
might occur.Comment: 29 pages, 24 figures, submitted to Ap
A Finite Difference Representation of Neutrino Radiation Hydrodynamics in Spherically Symmetric General Relativistic Space-Time
We present an implicit finite difference representation for general
relativistic radiation hydrodynamics in spherical symmetry. Our code,
Agile-Boltztran, solves the Boltzmann transport equation for the angular and
spectral neutrino distribution functions in self-consistent simulations of
stellar core collapse and postbounce evolution. It implements a dynamically
adaptive grid in comoving coordinates. Most macroscopically interesting
physical quantities are defined by expectation values of the distribution
function. We optimize the finite differencing of the microscopic transport
equation for a consistent evolution of important expectation values. We test
our code in simulations launched from progenitor stars with 13 solar masses and
40 solar masses. ~0.5 s after core collapse and bounce, the protoneutron star
in the latter case reaches its maximum mass and collapses further to form a
black hole. When the hydrostatic gravitational contraction sets in, we find a
transient increase in electron flavor neutrino luminosities due to a change in
the accretion rate. The muon- and tauon-neutrino luminosities and rms energies,
however, continue to rise because previously shock-heated material with a
non-degenerate electron gas starts to replace the cool degenerate material at
their production site. We demonstrate this by supplementing the concept of
neutrinospheres with a more detailed statistical description of the origin of
escaping neutrinos. We compare the evolution of the 13 solar mass progenitor
star to simulations with the MGFLD approximation, based on a recently developed
flux limiter. We find similar results in the postbounce phase and validate this
MGFLD approach for the spherically symmetric case with standard input physics.Comment: reformatted to 63 pages, 24 figures, to be published in ApJ
Cusp Anomalous dimension and rotating open strings in AdS/CFT
In the context of AdS/CFT we provide analytical support for the proposed
duality between a Wilson loop with a cusp, the cusp anomalous dimension, and
the meson model constructed from a rotating open string with high angular
momentum. This duality was previously studied using numerical tools in [1]. Our
result implies that the minimum of the profile function of the minimal area
surface dual to the Wilson loop, is related to the inverse of the bulk
penetration of the dual string that hangs from the quark--anti-quark pair
(meson) in the gauge theory.Comment: enhanced text, fixed tipos, reference added. Same results and
conclusions. arXiv admin note: text overlap with arXiv:1405.7388 by other
author
R\'enyi entanglement entropies in quantum dimer models : from criticality to topological order
Thanks to Pfaffian techniques, we study the R\'enyi entanglement entropies
and the entanglement spectrum of large subsystems for two-dimensional
Rokhsar-Kivelson wave functions constructed from a dimer model on the
triangular lattice. By including a fugacity on some suitable bonds, one
interpolates between the triangular lattice (t=1) and the square lattice (t=0).
The wave function is known to be a massive topological liquid for
whereas it is a gapless critical state at t=0. We mainly consider two
geometries for the subsystem: that of a semi-infinite cylinder, and the
disk-like setup proposed by Kitaev and Preskill [Phys. Rev. Lett. 96, 110404
(2006)]. In the cylinder case, the entropies contain an extensive term --
proportional to the length of the boundary -- and a universal sub-leading
constant . Fitting these cylinder data (up to a perimeter of L=32
sites) provides with a very high numerical accuracy ( at t=1 and
at ). In the topological liquid phase we find
, independent of the fugacity and the R\'enyi parameter
. At t=0 we recover a previously known result,
for . In the disk-like geometry --
designed to get rid of the boundary contributions -- we find an entropy in the whole massive phase whatever , in agreement with
the result of Flammia {\it et al.} [Phys. Rev. Lett. 103, 261601 (2009)]. Some
results for the gapless limit are discussed.Comment: 33 pages, 17 figures, minor correction
On the Importance of the Equation of State for the Neutrino-Driven Supernova Explosion Mechanism
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]Comment: 21 pages, 22 figures, accepted for publication in Ap
- …