107 research outputs found
Symmetry energy, neutron skin, and neutron star radius from chiral effective field theory interactions
We discuss neutron matter calculations based on chiral effective field theory
interactions and their predictions for the symmetry energy, the neutron skin of
208 Pb, and for the radius of neutron stars.Comment: 7 pages, 8 figures, short review article, to appear in EPJA special
issue on symmetry energ
Chiral interactions up to next-to-next-to-next-to-leading order and nuclear saturation
We present an efficient Monte Carlo framework for perturbative calculations
of infinite nuclear matter based on chiral two-, three-, and four-nucleon
interactions. The method enables the incorporation of all many-body
contributions in a straightforward and transparent way, and makes it possible
to extract systematic uncertainty estimates by performing order-by-order
calculations in the chiral expansion as well as the many-body expansion. The
versatility of this new framework is demonstrated by applying it to chiral
low-momentum interactions, exhibiting a very good many-body convergence up to
fourth order. Following these benchmarks, we explore new chiral interactions up
to next-to-next-to-next-to-leading order (NLO). Remarkably, simultaneous
fits to the triton and to saturation properties can be achieved, while all
three-nucleon low-energy couplings remain natural. The theoretical
uncertainties of nuclear matter are significantly reduced when going from
next-to-next-to-leading order to NLO.Comment: published version, incl. supplemental materia
Pairing in neutron matter: New uncertainty estimates and three-body forces
We present solutions of the BCS gap equation in the channels and
in neutron matter based on nuclear interactions derived
within chiral effective field theory (EFT). Our studies are based on a
representative set of nonlocal nucleon-nucleon (NN) plus three-nucleon (3N)
interactions up to next-to-next-to-next-to-leading order (NLO) as well as
local and semilocal chiral NN interactions up to NLO and NLO,
respectively. In particular, we investigate for the first time the impact of
subleading 3N forces at NLO on pairing gaps and also derive uncertainty
estimates by taking into account results for pairing gaps at different orders
in the chiral expansion. Finally, we discuss different methods for obtaining
self-consistent solutions of the gap equation. Besides the widely-used
quasi-linear method by Khodel et al. we demonstrate that the modified Broyden
method is well applicable and exhibits a robust convergence behavior. In
contrast to Khodel's method it is based on a direct iteration of the gap
equation without imposing an auxiliary potential and is straightforward to
implement
Neutron matter from chiral two- and three-nucleon calculations up to NLO
Neutron matter is an ideal laboratory for nuclear interactions derived from
chiral effective field theory since all contributions are predicted up to
next-to-next-to-next-to-leading order (NLO) in the chiral expansion. By
making use of recent advances in the partial-wave decomposition of three-
nucleon (3N) forces, we include for the first time NLO 3N interactions in
many-body perturbation theory (MBPT) up to third order and in self-consistent
Green's function theory (SCGF). Using these two complementary many-body
frameworks we provide improved predictions for the equation of state of neutron
matter at zero temperature and also analyze systematically the many-body
convergence for different chiral EFT interactions. Furthermore, we present an
extension of the normal-ordering framework to finite temperatures. These
developments open the way to improved calculations of neutron-rich matter
including estimates of theoretical uncertainties for astrophysical
applications.Comment: minor changes, published versio
Neutron matter at next-to-next-to-next-to-leading order in chiral effective field theory
Neutron matter presents a unique system for chiral effective field theory
(EFT), because all many-body forces among neutrons are predicted to
next-to-next-to-next-to-leading order (N3LO). We present the first complete
N3LO calculation of the neutron matter energy. This includes the subleading
three-nucleon (3N) forces for the first time and all leading four-nucleon (4N)
forces. We find relatively large contributions from N3LO 3N forces. Our results
provide constraints for neutron-rich matter in astrophysics with controlled
theoretical uncertainties.Comment: 5 pages, 4 figures; improved version, 3N ring and 2pi-contact
contributions corrected, conclusions unchanged; v3: minor changes, published
versio
Neutron matter from chiral effective field theory interactions
The neutron-matter equation of state constrains the properties of many
physical systems over a wide density range and can be studied systematically
using chiral effective field theory (EFT). In chiral EFT, all many-body forces
among neutrons are predicted to next-to-next-to-next-to-leading order (N3LO).
We present details and additional results of the first complete N3LO
calculation of the neutron-matter energy, which includes the subleading
three-nucleon as well as the leading four-nucleon forces, and provides
theoretical uncertainties. In addition, we discuss the impact of our results
for astrophysics: for the supernova equation of state, the symmetry energy and
its density derivative, and for the structure of neutron stars. Finally, we
give a first estimate for the size of the N3LO many-body contributions to the
energy of symmetric nuclear matter, which shows that their inclusion will be
important in nuclear structure calculations.Comment: published version; 21 pages, 11 figures, 5 table
Nuclear forces and their impact on neutron-rich nuclei and neutron-rich matter
We review the impact of nuclear forces on matter at neutron-rich extremes.
Recent results have shown that neutron-rich nuclei become increasingly
sensitive to three-nucleon forces, which are at the forefront of theoretical
developments based on effective field theories of quantum chromodynamics. This
includes the formation of shell structure, the spectroscopy of exotic nuclei,
and the location of the neutron dripline. Nuclear forces also constrain the
properties of neutron-rich matter, including the neutron skin, the symmetry
energy, and the structure of neutron stars. We first review our understanding
of three-nucleon forces and show how chiral effective field theory makes unique
predictions for many-body forces. Then, we survey results with three-nucleon
forces in neutron-rich oxygen and calcium isotopes and neutron-rich matter,
which have been explored with a range of many-body methods. Three-nucleon
forces therefore provide an exciting link between theoretical, experimental and
observational nuclear physics frontiers.Comment: 28 pages, 13 figures, 1 tabl
Uncertainties in constraining low-energy constants from H decay
We discuss the uncertainties in constraining low-energy constants of chiral
effective field theory from H decay. The half-life is very
precisely known, so that the Gamow-Teller matrix element has been used to fit
the coupling of the axial-vector current to a short-range two-nucleon
pair. Because the same coupling also describes the leading one-pion-exchange
three-nucleon force, this in principle provides a very constraining fit,
uncorrelated with the H binding energy fit used to constrain another
low-energy coupling in three-nucleon forces. However, so far such H
half-life fits have only been performed at a fixed cutoff value. We show that
the cutoff dependence due to the regulators in the axial-vector two-body
current can significantly affect the Gamow-Teller matrix elements and
consequently also the extracted values for the coupling constant. The
degree of the cutoff dependence is correlated with the softness of the employed
NN interaction. As a result, present three-nucleon forces based on a fit to
H decay underestimate the uncertainty in . We explore a range
of values that is compatible within cutoff variation with the
experimental H half-life and estimate the resulting uncertainties for
many-body systems by performing calculations of symmetric nuclear matter.Comment: 9 pages, 11 figures, published version, includes Erratum, which
corrects Figs. 2-6 due to the incorrect c_D relation between 3N forces and
two-body currents use
Constraints on neutron star radii based on chiral effective field theory interactions
We show that microscopic calculations based on chiral effective field theory
interactions constrain the properties of neutron-rich matter below nuclear
densities to a much higher degree than is reflected in commonly used equations
of state. Combined with observed neutron star masses, our results lead to a
radius R = 9.7 - 13.9 km for a 1.4 M_{solar} star, where the theoretical range
is due, in about equal amounts, to uncertainties in many-body forces and to the
extrapolation to high densities.Comment: 4 pages, 4 figures; NORDITA-2010-4
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