186 research outputs found
Dense matter equation of state and neutron star properties from nuclear theory and experiment
The equation of state of dense matter determines the structure of neutron
stars, their typical radii, and maximum masses. Recent improvements in
theoretical modeling of nuclear forces from the low-energy effective field
theory of QCD has led to tighter constraints on the equation of state of
neutron-rich matter at and somewhat above the densities of atomic nuclei, while
the equation of state and composition of matter at high densities remains
largely uncertain and open to a multitude of theoretical speculations. In the
present work we review the latest advances in microscopic modeling of the
nuclear equation of state and demonstrate how to consistently include also
empirical nuclear data into a Bayesian posterior probability distribution for
the model parameters. Derived bulk neutron star properties such as radii,
moments of inertia, and tidal deformabilities are computed, and we discuss as
well the limitations of our modeling.Comment: 9 pages, 5 figures. To appear in the AIP Proceedings of the
Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era
of Gravitational Wave Astronomy, Jan. 3-7, Xiamen, Chin
Proton pairing in neutron stars from chiral effective field theory
We study the proton pairing gap in beta-equilibrated neutron star
matter within the framework of chiral effective field theory. We focus on the
role of three-body forces, which strongly modify the effective proton-proton
spin-singlet interaction in dense matter. We find that three-body forces
generically reduce both the size of the pairing gap and the maximum density at
which proton pairing may occur. The pairing gap is computed within BCS theory,
and model uncertainties are estimated by varying the nuclear potential and the
choice of single-particle spectrum in the gap equation. We find that a
second-order perturbative treatment of the single-particle spectrum suppresses
the proton pairing gap relative to the use of a free spectrum. We
estimate the critical temperature for the onset of proton superconductivity to
be K, which is consistent with previous
theoretical results in the literature and marginally within the range deduced
from a recent Bayesian analysis of neutron star cooling observations.Comment: 8 pages, 9 figure
Hans Bethe: The Nuclear Many Body Problem
We discuss the work of Hans Bethe and others in formulating a theoretical
foundation for the nuclear shell model. Written for a general audience, this
article describes the evolution from Brueckner's reaction matrix theory to the
Moszkowski-Scott separation method and ultimately to the Reference Spectrum
method of Bethe, Brandow, and Petschek. We also discuss connections with the
recently developed low momentum nucleon-nucleon interactions.Comment: 25 pages, 15 figures, In "Hans Bethe and His Physics" (World
Scientific, Singapore, 2006
Divergence of the isospin-asymmetry expansion of the nuclear equation of state in many-body perturbation theory
The isospin-asymmetry dependence of the nuclear matter equation of state
obtained from microscopic chiral two- and three-body interactions in
second-order many-body perturbation theory is examined in detail. The
quadratic, quartic and sextic coefficients in the Maclaurin expansion of the
free energy per particle of infinite homogeneous nuclear matter with respect to
the isospin asymmetry are extracted numerically using finite differences, and
the resulting polynomial isospin-asymmetry parametrizations are compared to the
full isospin-asymmetry dependence of the free energy. It is found that in the
low-temperature and high-density regime where the radius of convergence of the
expansion is generically zero, the inclusion of higher-order terms beyond the
leading quadratic approximation leads overall to a significantly poorer
description of the isospin-asymmetry dependence. In contrast, at high
temperatures and densities well below nuclear saturation density, the
interaction contributions to the higher-order coefficients are negligible and
the deviations from the quadratic approximation are predominantly from the
noninteracting term in the many-body perturbation series. Furthermore, we
extract the leading logarithmic term in the isospin-asymmetry expansion of the
equation of state at zero temperature from the analysis of linear combinations
of finite differences. It is shown that the logarithmic term leads to a
considerably improved description of the isospin-asymmetry dependence at zero
temperature.Comment: 14 pages, 9 figures, 2 tables, some minor changes, references
updated, matches published versio
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