1,934 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
In-Medium Similarity Renormalization Group for Nuclei
We present a new ab-initio method that uses similarity renormalization group
(SRG) techniques to continuously diagonalize nuclear many-body Hamiltonians. In
contrast with applications of the SRG to two- and three-nucleon interactions in
free space, we perform the SRG evolution "in medium" directly in the -body
system of interest. The in-medium approach has the advantage that one can
approximately evolve -body operators using only two-body machinery
based on normal-ordering techniques. The method is nonperturbative and can be
tailored to problems ranging from the diagonalization of closed-shell nuclei to
the construction of effective valence shell-model Hamiltonians and operators.
We present first results for the ground-state energies of He, O and
Ca, which have accuracies comparable to coupled-cluster calculations.Comment: 4pages, 4 figures, to be published in PR
Low-momentum interactions for nuclei
We show how the renormalization group is used to construct a low-momentum
nucleon-nucleon interaction V_{low k}, which unifies all potential models used
in nuclear structure calculations. V_{low k} can be directly applied to the
nuclear shell model or to nucleonic matter without a G matrix resummation. It
is argued that V_{low k} parameterizes a high-order chiral effective field
theory two-nucleon force. We use cutoff dependence as a tool to assess the
error in the truncation of nuclear forces to two-nucleon interactions and
introduce a low-momentum three-nucleon force, which regulates A=3,4 binding
energies. The adjusted three-nucleon interaction is perturbative for small
cutoffs. In contrast to other precision interactions, the error due to missing
many-body forces can be estimated, when V_{low k} and the corresponding
three-nucleon force are used in nuclear structure calculations and the cutoff
is varied.Comment: 10 pages, 5 figures, talk at INT workshop on Nuclear Forces and the
Quantum Many-Body Problem, Seattle, October 200
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 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
From low-momentum interactions to nuclear structure
We present an overview of low-momentum two-nucleon and many-body interactions
and their use in calculations of nuclei and infinite matter. The softening of
phenomenological and effective field theory (EFT) potentials by renormalization
group (RG) transformations that decouple low and high momenta leads to greatly
enhanced convergence in few- and many-body systems while maintaining a
decreasing hierarchy of many-body forces. This review surveys the RG-based
technology and results, discusses the connections to chiral EFT, and clarifies
various misconceptions.Comment: 76 pages, 57 figures, two figures updated, 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
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