113 research outputs found
Numerical models for stationary superfluid neutron stars in general relativity with realistic equations of state
We present a numerical model for uniformly rotating superfluid neutron stars,
for the first time with realistic microphysics including entrainment, in a
fully general relativistic framework. We compute stationary and axisymmetric
configurations of neutron stars composed of two fluids, namely superfluid
neutrons and charged particles (protons and electrons), rotating with different
rates around a common axis. Both fluids are coupled by entrainment, a
non-dissipative interaction which in case of a non-vanishing relative velocity
between the fluids, causes the fluid momenta being not aligned with the
respective fluid velocities. We extend the formalism by Comer and Joynt (2003)
in order to calculate the equation of state (EoS) and entrainment parameters
for an arbitrary relative velocity. The resulting entrainment matrix fulfills
all necessary sum rules and in the limit of small relative velocity our results
agree with Fermi liquid theory ones, derived to lowest order in the velocity.
This formalism is applied to two new nuclear equations of state which are
implemented in the numerical model. We are able to obtain precise equilibrium
configurations. Resulting density profiles and moments of inertia are discussed
employing both EoSs, showing the impact of entrainment and the dependence on
the EoS.Comment: 18 pages, 10 figures, minor changes to match published version in
PRD, a typo present in Eq.A1 in the published version has been correcte
Influence of pions and hyperons on stellar black hole formation
We present numerical simulations of stellar core-collapse with spherically
symmetric, general relativistic hydrodynamics up to black hole formation. Using
the CoCoNuT code, with a newly developed grey leakage scheme for the neutrino
treatment, we investigate the effects of including pions and \Lambda-hyperons
into the equation of state at high densities and temperatures on the black hole
formation process. Results show non-negligible differences between the models
with reference equation of state without any additional particles and models
with the extended ones. For the latter, the maximum masses supported by the
proto-neutron star are smaller and the collapse to a black hole occurs earlier.
A phase transition to hyperonic matter is observed when the progenitor allows
for a high enough accretion rate onto the proto-neutron star. Rough estimates
of neutrino luminosity from these collapses are given, too.Comment: 22 pages, 10 figures. Minor change
Global numerical simulations of the rise of vortex-mediated pulsar glitches in full general relativity
In this paper, we study in detail the role of general relativity on the
global dynamics of giant pulsar glitches as exemplified by Vela. For this
purpose, we carry out numerical simulations of the spin up triggered by the
sudden unpinning of superfluid vortices. In particular, we compute the exchange
of angular momentum between the core neutron superfluid and the rest of the
star within a two-fluid model including both (non-dissipative) entrainment
effects and (dissipative) mutual friction forces. Our simulations are based on
a quasi-stationary approach using realistic equations of state (EoSs). We show
that the evolution of the angular velocities of both fluids can be accurately
described by an exponential law. The associated characteristic rise time
, which can be precisely computed from stationary
configurations only, has a form similar to that obtained in the Newtonian
limit. However, general relativity changes the structure of the star and leads
to additional couplings between the fluids due to frame-dragging effects. As a
consequence, general relativity can have a large impact on the actual value of
: the errors incurred by using Newtonian gravity are thus
found to be as large as for the models considered. Values of the
rise time are calculated for Vela and compared with current observational
limits. Finally, we study the amount of gravitational waves emitted during a
glitch. Simple expressions are obtained for the corresponding characteristic
amplitudes and frequencies. The detectability of glitches through gravitational
wave observatories is briefly discussed.Comment: 19 pages, 12 figures, minor changes to match version to be published
in MNRA
Goldstone bosons in the color-flavor locked phase
We study pseudoscalar meson excitations in the color-flavor locked phase
within a Nambu-Jona-Lasinio-type model by calculating diquark loops.Comment: Talk given by V.W. at the Helmholtz International Summer School
"Dense Matter In Heavy Ion Collisions and Astrophysics", Dubna, August 21 -
September 1, 2006; 4 pages, to appear in the proceeding
Pseudoscalar Goldstone bosons in the color-flavor locked phase at moderate densities
The properties of the pseudoscalar Goldstone bosons in the color-flavor
locked phase at moderate densities are studied within a model of the
Nambu--Jona-Lasinio type. The Goldstone bosons are constructed explicitly by
solving the Bethe-Salpeter equation for quark-quark scattering in random phase
approximation. Main focus of our investigations are (i) the weak decay constant
in the chiral limit, (ii) the masses of the flavored (pseudo-) Goldstone bosons
for non-zero but equal quark masses, (iii) their masses and effective chemical
potentials for non-equal quark masses, and (iv) the onset of kaon condensation.
We compare our results with the predictions of the low-energy effective field
theory. The deviations from results obtained in the weak-coupling limit are
discussed in detail.Comment: 18 pages, 12 figure
Equations of state for supernovae and compact stars
A review is given of various theoretical approaches for the equation of state (EoS) of dense matter, relevant for the description of core-collapse supernovae, compact stars, and compact star mergers. The emphasis is put on models that are applicable to all of these scenarios. Such EoS models have to cover large ranges in baryon number density, temperature, and isospin asymmetry. The characteristics of matter change dramatically within these ranges, from a mixture of nucleons, nuclei, and electrons to uniform, strongly interacting matter containing nucleons, and possibly other particles such as hyperons or quarks. As the development of an EoS requires joint efforts from many directions, different theoretical approaches are considered and relevant experimental and observational constraints which provide insights for future research are discussed. Finally, results from applications of the discussed EoS models are summarized
How Well Do We Know The Supernova Equation of State?
We give an overview about equations of state (EOS) which are currently available for simulations of core-collapse supernovae and neutron star mergers. A few selected important aspects of the EOS, such as the symmetry energy, the maximum mass of neutron stars, and cluster formation, are confronted with constraints from experiments and astrophysical observations. There are just very few models which are compatible even with this very restricted set of constraints. These remaining models illustrate the uncertainty of the uniform nuclear matter EOS at high densities. In addition, at finite temperatures the medium modifications of nuclear clusters represent a conceptual challenge. In conclusion, there has been significant development in the recent years, but there is still need for further improved general purpose EOS tables
Generalised description of Neutron Star matter with nucleonic Relativistic Density Functional
In this work, we propose a meta-modelling technique to nuclear matter on the
basis of a relativistic density functional with density-dependent couplings.
Identical density dependence for the couplings both in the isoscalar and
isovector sectors is employed. We vary the coupling parameters of the model to
capture the uncertainties of the empirical nuclear matter parameters at
saturation. Then, we construct a large ensemble of unified equations of state
in a consistent manner both for clusterized and uniform matter in
-equilibrium at zero temperature. Finally, we calculate neutron star
properties to check the consistency with astrophysical observations within a
Bayesian framework. Out of the different sets of astrophysical data employed,
constraint on tidal deformability from the GW170817 event was found to be the
most stringent in the posteriors of different neutron star properties explored
in the present study. We demonstrate in detail the impact of the isovector
incompressibility () on high-density matter that leads to a
considerable variation in the composition of neutron star matter. A couple of
selected models with extreme values of , which satisfy various modern
nuclear physics and neutron star astrophysics constraints, are uploaded in the
\textsc{CompOSE} \cite{Typel:2013rza} database for use by the community
Quantum corrections to the effective neutrino mass operator in 5D MSSM
We discuss in detail a five-dimensional Minimal Supersymmetric Standard Model
compactified on extended by the effective Majorana neutrino mass
operator. We study the evolution of neutrino masses and mixings. Masses and
angles, in particular the atmospheric mixing angle , can be
significantly lowered at high energies with respect to their value at low
energy.Comment: 23 pages, 13 figure
The explosion mechanism of core-collapse supernovae: progress in supernova theory and experiments
The explosion of core-collapse supernova depends on a sequence of events
taking place in less than a second in a region of a few hundred kilometers at
the center of a supergiant star, after the stellar core approaches the
Chandrasekhar mass and collapses into a proto-neutron star, and before a shock
wave is launched across the stellar envelope. Theoretical efforts to understand
stellar death focus on the mechanism which transforms the collapse into an
explosion. Progress in understanding this mechanism is reviewed with particular
attention to its asymmetric character. We highlight a series of successful
studies connecting observations of supernova remnants and pulsars properties to
the theory of core-collapse using numerical simulations. The encouraging
results from first principles models in axisymmetric simulations is tempered by
new puzzles in 3D. The diversity of explosion paths and the dependence on the
pre-collapse stellar structure is stressed, as well as the need to gain a
better understanding of hydrodynamical and MHD instabilities such as SASI and
neutrino-driven convection. The shallow water analogy of shock dynamics is
presented as a comparative system where buoyancy effects are absent. This
dynamical system can be studied numerically and also experimentally with a
water fountain. The potential of this complementary research tool for supernova
theory is analyzed. We also review its potential for public outreach in science
museums.Comment: 19 pages, 6 figures, invited review accepted for publication in PAS
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