2,436 research outputs found
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
Chiral effective field theory (EFT) enables a systematic description of
low-energy hadronic interactions with controlled theoretical uncertainties. For
strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of
the most accurate solutions, but they require as input local potentials. We
have recently constructed local chiral nucleon-nucleon (NN) interactions up to
next-to-next-to-leading order (NLO). Chiral EFT naturally predicts
consistent many-body forces. In this paper, we consider the leading chiral
three-nucleon (3N) interactions in local form. These are included in auxiliary
field diffusion Monte Carlo (AFDMC) simulations. We present results for the
equation of state of neutron matter and for the energies and radii of neutron
drops. In particular, we study the regulator dependence at the Hartree-Fock
level and in AFDMC and find that present local regulators lead to less
repulsion from 3N forces compared to the usual nonlocal regulators.Comment: 10 pages, 8 figures, 1 table, 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
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
Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials
Chiral effective field theory is a framework to derive systematic nuclear
interactions. It is based on the symmetries of quantum chromodynamics and
includes long-range pion physics explicitly, while shorter-range physics is
expanded in a general operator basis. The number of low-energy couplings at a
particular order in the expansion can be reduced by exploiting the fact that
nucleons are fermions and therefore obey the Pauli exclusion principle. The
antisymmetry permits the selection of a subset of the allowed contact operators
at a given order. When local regulators are used for these short-range
interactions, however, this "Fierz rearrangement freedom" is violated. In this
paper, we investigate the impact of this violation at leading order (LO) in the
chiral expansion. We construct LO and next-to-leading order (NLO) potentials
for all possible LO-operator pairs and study their reproduction of phase
shifts, the He ground-state energy, and the neutron-matter energy at
different densities. We demonstrate that the Fierz rearrangement freedom is
partially restored at NLO where subleading contact interactions enter. We also
discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure
The chiral condensate in neutron matter
We calculate the chiral condensate in neutron matter at zero temperature
based on nuclear forces derived within chiral effective field theory. Two-,
three- and four-nucleon interactions are included consistently to
next-to-next-to-next-to-leading order (N3LO) of the chiral expansion. We find
that the interaction contributions lead to a modest increase of the condensate,
thus impeding the restoration of chiral symmetry in dense matter and making a
chiral phase transition in neutron-rich matter unlikely for densities that are
not significantly higher than nuclear saturation density.Comment: published version, 6 pages, 4 figure
Chiral Three-Nucleon Interactions in Light Nuclei, Neutron- Scattering, and Neutron Matter
We present quantum Monte Carlo calculations of light nuclei, neutron-
scattering, and neutron matter using local two- and three-nucleon ()
interactions derived from chiral effective field theory up to
next-to-next-to-leading order (NLO). The two undetermined low-energy
couplings are fit to the He binding energy and, for the first time, to the
spin-orbit splitting in the neutron- -wave phase shifts.
Furthermore, we investigate different choices of local -operator structures
and find that chiral interactions at NLO are able to simultaneously
reproduce the properties of systems and of neutron matter, in
contrast to commonly used phenomenological interactions.Comment: 5 pages, 3 figures, 1 table - updated version: small wording changes,
one reference chang
Quantum Monte Carlo calculations of light nuclei with local chiral two- and three-nucleon interactions
Local chiral effective field theory interactions have recently been developed
and used in the context of quantum Monte Carlo few- and many-body methods for
nuclear physics. In this work, we go over detailed features of local chiral
nucleon-nucleon interactions and examine their effect on properties of the
deuteron, paying special attention to the perturbativeness of the expansion. We
then turn to three-nucleon interactions, focusing on operator ambiguities and
their interplay with regulator effects. We then discuss the nuclear Green's
function Monte Carlo method, going over both wave-function correlations and
approximations for the two- and three-body propagators. Following this, we
present a range of results on light nuclei: Binding energies and distribution
functions are contrasted and compared, starting from several different
microscopic interactions.Comment: 21 pages, 14 figures, published version, Editor's Suggestio
Large-cutoff behavior of local chiral effective field theory interactions
Interactions from chiral effective field theory have been successfully
employed in a broad range of \textit{ab initio} calculations of nuclei and
nuclear matter, but it has been observed that most results of few- and
many-body calculations experience a substantial residual regulator and cutoff
dependence. In this work, we investigate the behavior of local chiral
potentials at leading order under variation of the cutoff scale for different
local regulators. When varying the cutoff, we require that the resulting
interaction produces no spurious bound states in the deuteron channel. We find
that, for a particular choice of leading-order operators, nucleon-nucleon phase
shifts and the deuteron ground-state energy converge to cutoff-independent
plateaus, for all regulator functions we investigate. This observation may
enable improved calculations with chiral Hamiltonians that also include
three-nucleon interactions.Comment: 10 pages, 6 figures, published versio
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