897 research outputs found

### Nucleon self-energies for supernova equations of state

Nucleon self-energies and interaction potentials in supernova (SN) matter,
which are known to have an important effect on nucleosynthesis conditions in SN
ejecta are investigated. Corresponding weak charged-current interaction rates
with unbound nucleons that are consistent with existing SN equations of state
(EOSs) are specified. The nucleon self-energies are made available online as
electronic tables. The discussion is mostly restricted to relativistic
mean-field models.
In the first part of the article, the generic properties of this class of
models at finite temperature and asymmetry are studied. It is found that the
quadratic expansion of the EOS in terms of asymmetry works reasonably well at
finite temperatures and deviations originate mostly from the kinetic part. The
interaction part of the symmetry energy is found to be almost temperature
independent. At low densities, the account of realistic nucleon masses requires
the introduction of a linear term in the expansion. Finally, it is shown that
the important neutron-to-proton potential difference is given approximately by
the asymmetry of the system and the interaction part of the zero-temperature
symmetry energy. The results of different interactions are then compared with
constraints from nuclear experiments and thereby the possible range of the
potential difference is limited.
In the second part, for a certain class of SN EOS models, the formation of
nuclei is considered. Only moderate modifications are found for the
self-energies of unbound nucleons that enter the weak charged-current
interaction rates. This is because in the present approach the binding energies
of bound states do not contribute to the single-particle energies of unbound
nucleons.Comment: 25 pages, 12 figures, v3: editorial corrections, matches published
versio

### The internal structure of neutron stars and white dwarfs, and the Jacobi virial equation. II

In a previous paper we have shown that the function \Gamma(M,
EOS)=\alpha\beta_{GR}/\Lambda^{0.9}(R) is constant (~ 0.4) for pre
main-sequence stars (PMS), white dwarfs (WD) and for some neutron star (NS)
models, where \alpha_{GR} and \beta_{GR} are the form-factors of the
gravitational potential energy and of the moment of inertia. To investigate the
structural evolution of another type of celestial bodies, we use the MESA code
to extend these calculations to gaseous planets. We show that this function is
conserved for all models during the whole planetary evolution and is
independent of the planet mass. We also analyse the cases for which this
function is not conserved during some stellar evolutionary phases. For the PMS
to the WD cooling sequences, we have found a connection between the strong
variations of \Gamma(M, EOS) during the intermediary evolutionary phases and
the specific nuclear power. A threshold for the specific nuclear power was
determined. Below this limit this function is invariant (~ 0.4) for these
models, i.e., at the initial and final stages (PMS and WD). Concerning NS, we
study the influence of the equation of state (EOS) on this function and refine
the exponent of the auxiliary function \Lambda(R) to be ~ 0.8. It is shown that
the function \Gamma(M, EOS) is also invariant (~ 0.4) and is independent of the
EOS and of the stellar mass. Therefore, we confirm that regardless of the final
products of the stellar evolution, NS or WD, they recover the initial value of
\Gamma(M, EOS) ~ 0.4 acquired at the PMS. Finally, we have introduced a
macroscopic stability "criterion" for neutron star models based on the
properties of the relativistic product \alpha\beta_{GR}.Comment: 6 pages, 5 figures, v3: editorial changes, identical to published
versio

### Consequences of simultaneous chiral symmetry breaking and deconfinement for the isospin symmetric phase diagram

The thermodynamic bag model (tdBag) has been applied widely to model quark
matter properties in both heavy-ion and astrophysics communities. Several
fundamental physics aspects are missing in tdBag, e.g., dynamical chiral
symmetry breaking (D$\chi$SB) and repulsions due to the vector interaction are
both included explicitly in the novel vBag quark matter model of Kl\"ahn and
Fischer (2015) (Astrophys. J. 810, 134 (2015)). An important feature of vBag is
the simultaneous D$\chi$SB and deconfinement, where the latter links vBag to a
given hadronic model for the construction of the phase transition. In this
article we discuss the extension to finite temperatures and the resulting phase
diagram for the isospin symmetric medium.Comment: 6 pages, 2 figures, Contribution to the Topical Issue Exploring
strongly interacting matter at high densities - NICA White Paper edited by
David Blaschke et a

### New Hyperon Equations of State for Supernovae and Neutron Stars in Density-dependent Hadron Field Theory

We develop new hyperon equation of state (EoS) tables for core-collapse
supernova simulations and neutron stars. These EoS tables are based on a
density-dependent relativistic hadron field theory where baryon-baryon
interaction is mediated by mesons, using the parameter set DD2 from Typel et
al. (2010) for nucleons. Furthermore, light and heavy nuclei along with the
interacting nucleons are treated in the nuclear statistical equilibrium model
of Hempel and Schaffner-Bielich which includes excluded volume effects. Of all
possible hyperons, we consider only the contribution of $\Lambda$s. We have
developed two variants of hyperonic EoS tables: in the np$\Lambda \phi$ case
the repulsive hyperon-hyperon interaction mediated by the strange $\phi$ meson
is taken into account, and in the np$\Lambda$ case it is not. The EoS tables
for the two cases encompass wide range of density ($10^{-12}$ to $\sim$ 1
fm$^{-3}$), temperature (0.1 to 158.48 MeV), and proton fraction (0.01 to
0.60). The effects of $\Lambda$ hyperons on thermodynamic quantities such as
free energy per baryon, pressure, or entropy per baryon are investigated and
found to be significant at high densities. The cold, $\beta$-equilibrated EoS
(with the crust included self-consistently) results in a 2.1 M$_{\odot}$
maximum mass neutron star for the np$\Lambda \phi$ case, whereas that for the
np$\Lambda$ case is 1.95 M$_{\odot}$. The np$\Lambda \phi$ EoS represents the
first supernova EoS table involving hyperons that is directly compatible with
the recently measured 2 M$_{\odot}$ neutron stars.Comment: 39 pages, 9 figures, 11 tables; matches published version, only minor
additions and editorial change

### Multi-dimensional Core-Collapse Supernova Simulations with Neutrino Transport

We present multi-dimensional core-collapse supernova simulations using the
Isotropic Diffusion Source Approximation (IDSA) for the neutrino transport and
a modified potential for general relativity in two different supernova codes:
FLASH and ELEPHANT. Due to the complexity of the core-collapse supernova
explosion mechanism, simulations require not only high-performance computers
and the exploitation of GPUs, but also sophisticated approximations to capture
the essential microphysics. We demonstrate that the IDSA is an elegant and
efficient neutrino radiation transfer scheme, which is portable to multiple
hydrodynamics codes and fast enough to investigate long-term evolutions in two
and three dimensions. Simulations with a 40 solar mass progenitor are presented
in both FLASH (1D and 2D) and ELEPHANT (3D) as an extreme test condition. It is
found that the black hole formation time is delayed in multiple dimensions and
we argue that the strong standing accretion shock instability before black hole
formation will lead to strong gravitational waves.Comment: 3 pages, proceedings for Nuclei in the Cosmos XIV, Niigata, Japan
(2016

### Two-Dimensional Core-Collapse Supernova Simulations with the Isotropic Diffusion Source Approximation for Neutrino Transport

The neutrino mechanism of core-collapse supernova is investigated via
non-relativistic, two-dimensional (2D), neutrino radiation-hydrodynamic
simulations. For the transport of electron flavor neutrinos, we use the
interaction rates defined by Bruenn (1985) and the isotropic diffusion source
approximation (IDSA) scheme, which decomposes the transported particles into
trapped particle and streaming particle components. Heavy neutrinos are
described by a leakage scheme. Unlike the "ray-by-ray" approach in some other
multi-dimensional supernova models, we use cylindrical coordinates and solve
the trapped particle component in multiple dimensions, improving the
proto-neutron star resolution and the neutrino transport in angular and
temporal directions. We provide an IDSA verification by performing 1D and 2D
simulations with 15 and 20 $M_\odot$ progenitors from Woosley et al.~(2007) and
discuss the difference of our IDSA results with those existing in the
literature. Additionally, we perform Newtonian 1D and 2D simulations from
prebounce core collapse to several hundred milliseconds postbounce with 11, 15,
21, and 27 $M_\odot$ progenitors from Woosley et al.~(2002) with the HS(DD2)
equation of state. General relativistic effects are neglected. We obtain robust
explosions with diagnostic energies $E_{\rm dig} \gtrsim 0.1- 0.5$~B for all
considered 2D models within approximately $100-300$ milliseconds after bounce
and find that explosions are mostly dominated by the neutrino-driven
convection, although standing accretion shock instabilities are observed as
well. We also find that the level of electron deleptonization during collapse
dramatically affect the postbounce evolution, e.g.~the ignorance of
neutrino-electron scattering during collapse will lead to a stronger explosion.Comment: 23 pages. Accepted for publication in Ap

### Quark-hadron mixed phases in protoneutron stars

We consider the possible formation of the quark hadron mixed phase in
protoneutron stars. We discuss two cases: the first one, corresponding to a
vanishingly small value of the surface tension of quark matter, is the well
known mixed phase in which the global electric charge neutrality condition is
imposed. In turn, this produces a non-constant pressure mixed phase. In the
second case, corresponding to very large values of the surface tension, the
charge neutrality condition holds only locally. However, the existence in
protoneutron star matter of an additional globally conserved charge, the lepton
number, allows for a new type of non-constant pressure mixed phase. We discuss
the properties of the new mixed phase and the possible effects of its formation
during the evolution of protoneutron stars.Comment: 6 pages, 2 figures, talk given at the the International Conference
SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200

### Towards generating a new supernova equation of state: A systematic analysis of cold hybrid stars

The hadron-quark phase transition in core-collapse supernovae (CCSNe) has the
potential to trigger explosions in otherwise nonexploding models. However,
those hybrid supernova equations of state (EOS) shown to trigger an explosion
do not support the observational 2 M$_\odot$ neutron star maximum mass
constraint. In this work, we analyze cold hybrid stars by the means of a
systematic parameter scan for the phase transition properties, with the aim to
develop a new hybrid supernova EOS. The hadronic phase is described with the
state-of-the-art supernova EOS HS(DD2), and quark matter by an EOS with a
constant speed of sound (CSS) of $c_{QM}^2=1/3$. We find promising cases which
meet the 2 M$_\odot$ criterion and are interesting for CCSN explosions. We show
that the very simple CSS EOS is transferable into the well-known thermodynamic
bag model, important for future application in CCSN simulations. In the second
part, the occurrence of reconfinement and multiple phase transitions is
discussed. In the last part, the influence of hyperons in our parameter scan is
studied. Including hyperons no change in the general behavior is found, except
for overall lower maximum masses. In both cases (with and without hyperons) we
find that quark matter with $c_{QM}^2=1/3$ can increase the maximum mass only
if reconfinement is suppressed or if quark matter is absolutely stable.Comment: 14 pages, 11 figures, v2: matches published versio

### Phase transitions in dense matter

As the density of matter increases, atomic nuclei disintegrate into nucleons
and, eventually, the nucleons themselves disintegrate into quarks. The phase
transitions (PT's) between these phases can vary from steep first order to
smooth crossovers, depending on certain conditions. First-order PT's with more
than one globally conserved charge, so-called non-congruent PT's, have
characteristic differences compared to congruent PT's. In this conference
proceeding we discuss the non-congruence of the quark deconfinement PT at high
densities and/or temperatures relevant for heavy-ion collisions, neutron stars,
proto-neutron stars, supernova explosions, and compact-star mergers.Comment: Proceedings of XXVIth International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions (Quark Matter 2017

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