3,824 research outputs found
Pre-supernova evolution, compact object masses and explosion properties of stripped binary stars
Most massive stars are born in binary or higher-order multiple systems and
exchange mass with a companion during their lives. In particular, the
progenitors of a large fraction of compact object mergers, and Galactic neutron
stars (NSs) and black holes (BHs) have been stripped off their envelopes by a
binary companion. Here, we study the evolution of single and stripped binary
stars up to core collapse with the stellar evolution code MESA and their final
fates with a parametric supernova (SN) model. We find that stripped binary
stars can have systematically different pre-SN structures compared to genuine
single stars and thus also different SN outcomes. The bases of these
differences are already established by the end of core helium burning and are
preserved up to core collapse. We find a non-monotonic pattern of NS and BH
formation as a function of CO core mass that is different in single and
stripped binary stars. In terms of initial masses, single stars of >35 Msun all
form BHs, while this transition is only at 70 Msun in stripped stars. On
average, stripped stars give rise to lower NS and BH masses, higher explosion
energies, higher kick velocities and higher nickel yields. Within a simplified
population synthesis model, we show that our results lead to a significant
reduction of the rates of BH-NS and BH-BH mergers with respect to typical
assumptions made on NS and BH formation. Therefore, we predict lower detection
rates of such merger events by, e.g., advanced LIGO than is often considered.
We further show how features in the NS-BH mass distribution of single and
stripped stars relate to the chirp-mass distribution of compact object mergers.
Further implications of our findings are discussed with respect to the missing
red-supergiant problem, a possible mass gap between NSs and BHs, X-ray binaries
and observationally inferred nickel masses from Type Ib/c and IIP Sne.
[abridged]Comment: 25 pages (incl. appendix), 17 figures, 2 tables; final version
accepted for publication in A&
Effect of bulk viscosity on Elliptic Flow near QCD phase transition
Effects of the bulk viscosity on the elliptic flow are studied. To introduce
a realistic equation of state and transport coefficients, we apply the results
of the lattice QCD and hadron resonance gas calculations for these quantities.
We found that the bulk viscosity acts in a non trivial manner on the elliptic
flow . The reduction of is more effective at low
compared to the case of shear viscosity, whereas at high , the situation
is reversed, leading to enhancement. We argue that this is caused by
the competition of the critical behaviors of the equation of state and the
transport coefficients. We further found that Grad's method with the 14 moments
approximation is not applicable to estimate the viscous effects for the
one-particle distribution function at the freeze out.Comment: 14 pages, 12 figure
Relativistic Dissipative Hydrodynamics: A Minimal Causal Theory
We present a new formalism for the theory of relativistic dissipative
hydrodynamics. Here, we look for the minimal structure of such a theory which
satisfies the covariance and causality by introducing the memory effect in
irreversible currents. Our theory has a much simpler structure and thus has
several advantages for practical purposes compared to the Israel-Stewart theory
(IS). It can readily be applied to the full three-dimensional hydrodynamical
calculations. We apply our formalism to the Bjorken model and the results are
shown to be analogous to the IS.Comment: 25 pages, 2 figures, Phys. Rev. C in pres
Influence of the Coulomb Interaction on the Chemical Equilibrium of Nuclear Systems at Break-Up
The importance of a Coulomb correction to the formalism proposed by Albergo
et al. for determining the temperatures of nuclear systems at break-up and the
ensities of free nucleon gases is discussed. While the proposed correction has
no effect on the temperatures extracted based on double isotope ratios, it
becomes non-negligible when such temperatures or densities of free nucleon
gases are extracted based on multiplicities of heavier fragments of different
atomic numbers
Ab initio phonon dispersion curves and interatomic force constants of barium titanate
The phonon dispersion curves of cubic BaTiO_3 have been computed within a
first-principles approach and the results compared to the experimental data.
The curves obtained are very similar to those reported for KNbO_3 by Yu and
Krakauer [Phys. Rev. Lett. 74, 4067 (1995)]. They reveal that correlated atomic
displacements along chains are at the origin of the ferroelectric
instability. A simplified model illustrates that spontaneous collective
displacements will occur when a dozen of aligned atoms are coupled. The
longitudinal interatomic force constant between nearest neighbour Ti and O
atoms is relatively weak in comparison to that between Ti atoms in adjacent
cells. The small coupling between Ti and O displacements seems however
necessary to reproduce a ferroelectric instability.Comment: 12 pages, 4 figure
Insight into nucleon structure from generalized parton distributions
The lowest three moments of generalized parton distributions are calculated
in full QCD and provide new insight into the behavior of nucleon
electromagnetic form factors, the origin of the nucleon spin, and the
transverse structure of the nucleon.Comment: 3 pages, Lattice2003(Theoretical developments
The electronic structure of the heavy fermion metal
The electronic structure of the first reported heavy fermion compound without
f-electrons LiV_2O_4 was studied by an ab-initio calculation method. In the
result of the trigonal splitting and d-d Coulomb interaction one electron of
the configuration of V ion is localized and the rest partially fills
a relatively broad conduction band. The effective Anderson impurity model was
solved by Non-Crossing-Approximation method, leading to an estimation for the
single-site Kondo energy scale T_K. Then, we show how the so-called exhaustion
phenomenon of Nozi\`eres for the Kondo lattice leads to a remarkable decrease
of the heavy-fermion (or coherence) energy scale (D
is the typical bandwidth), comparable to the experimental result.Comment: 4 pages, RevTeX; 3 figures in format .eps. submitted to PR
Generalized parton distributions and structure functions from full lattice QCD
We present here the latest results from the QCDSF collaboration for (moments
of) structure functions and generalized form factors in full QCD with Nf=2
O(a)-improved Wilson fermions based on simulations closer to the chiral and
continuum limit.Comment: Talks presented by D.Pleiter and J.Zanotti at Lattice2004(weak),
Fermilab, June 21-26, 2004, 6 pages, 9 figure
Moments of nucleon spin-dependent generalized parton distributions
We present a lattice measurement of the first two moments of the
spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling
constant and the second moment of the spin-dependent forward parton
distribution. The measurements are done in full QCD using Wilson fermions. In
addition, we also present results from a first exploratory study of full QCD
using Asqtad sea and domain-wall valence fermions.Comment: Lattice2003(Theory), 3 pages, 3 figures, to appear in the Proceedings
of Lattice 200
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