1,902 research outputs found
Three-body forces and proton-rich nuclei
We present the first study of three-nucleon (3N) forces for proton-rich
nuclei along the N=8 and N=20 isotones. Our results for the ground-state
energies and proton separation energies are in very good agreement with
experiment where available, and with the empirical isobaric multiplet mass
equation. We predict the spectra for all N=8 and N=20 isotones to the proton
dripline, which agree well with experiment for 18Ne, 19Na, 20Mg and 42Ti. In
all other cases, we provide first predictions based on nuclear forces. Our
results are also very promising for studying isospin symmetry breaking in
medium-mass nuclei based on chiral effective field theory.Comment: 5 pages, 4 figures, minor changes, published versio
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
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
Three-body forces and shell structure in calcium isotopes
Understanding and predicting the formation of shell structure from nuclear
forces is a central challenge for nuclear physics. While the magic numbers
N=2,8,20 are generally well understood, N=28 is the first standard magic number
that is not reproduced in microscopic theories with two-nucleon forces. In this
Letter, we show that three-nucleon forces give rise to repulsive interactions
between two valence neutrons that are key to explain 48Ca as a magic nucleus,
with a high 2+ excitation energy and a concentrated magnetic dipole transition
strength. The repulsive three-nucleon mechanism improves the agreement with
experimental binding energies.Comment: 5 pages, 4 figures; improved version and added coupled-cluster
benchmark; published versio
Three-nucleon forces and spectroscopy of neutron-rich calcium isotopes
We study excited-state properties of neutron-rich calcium isotopes based on
chiral two- and three-nucleon interactions. We first discuss the details of our
many-body framework, investigate convergence properties, and for two-nucleon
interactions benchmark against coupled-cluster calculations. We then focus on
the spectroscopy of 47-56Ca, finding that with both 3N forces and an extended
pfg9/2 valence space, we obtain a good level of agreement with experiment. We
also study electromagnetic transitions and find that experimental data are well
described by our calculations. In addition, we provide predictions for
unexplored properties of neutron-rich calcium isotopes.Comment: 15 pages, 22 figures, published versio
Dispersion and decay of collective modes in neutron star cores
We calculate the frequencies of collective modes of neutrons, protons and
electrons in the outer core of neutron stars. The neutrons and protons are
treated in a hydrodynamic approximation and the electrons are regarded as
collisionless. The coupling of the nucleons to the electrons leads to Landau
damping of the collective modes and to significant dispersion of the low-lying
modes. We investigate the sensitivity of the mode frequencies to the strength
of entrainment between neutrons and protons, which is not well characterized.
The contribution of collective modes to the thermal conductivity is evaluated.Comment: 10 pages, 4 figure
Three-body forces and the limit of oxygen isotopes
The limit of neutron-rich nuclei, the neutron drip-line, evolves regularly
from light to medium-mass nuclei except for a striking anomaly in the oxygen
isotopes. This anomaly is not reproduced in shell-model calculations derived
from microscopic two-nucleon forces. Here, we present the first microscopic
explanation of the oxygen anomaly based on three-nucleon forces that have been
established in few-body systems. This leads to repulsive contributions to the
interactions among excess neutrons that change the location of the neutron
drip-line from O to the experimentally observed O. Since the
mechanism is robust and general, our findings impact the prediction of the most
neutron-rich nuclei and the synthesis of heavy elements in neutron-rich
environments.Comment: 4 pages, 4 figures, to be published in PR
Cooling of Akmal-Pandharipande-Ravenhall neutron star models
We study the cooling of superfluid neutron stars whose cores consist of
nucleon matter with the Akmal-Pandharipande-Ravenhall equation of state. This
equation of state opens the powerful direct Urca process of neutrino emission
in the interior of most massive neutron stars. Extending our previous studies
(Gusakov et al. 2004a, Kaminker et al. 2005), we employ phenomenological
density-dependent critical temperatures T_{cp}(\rho) of strong singlet-state
proton pairing (with the maximum T_{cp}^{max} \sim 7e9 K in the outer stellar
core) and T_{cnt}(\rho) of moderate triplet-state neutron pairing (with the
maximum T_{cnt}^{max} \sim 6e8 K in the inner core). Choosing properly the
position of T_{cnt}^{max} we can obtain a representative class of massive
neutron stars whose cooling is intermediate between the cooling enhanced by the
neutrino emission due to Cooper pairing of neutrons in the absence of the
direct Urca process and the very fast cooling provided by the direct Urca
process non-suppressed by superfluidity.Comment: 9 pages, 6 figures; accepted for publication in MNRA
Exploring sd-shell nuclei from two- and three-nucleon interactions with realistic saturation properties
We study ground- and excited-state properties of all sd-shell nuclei with
neutron and proton numbers 8 <= N,Z <= 20, based on a set of low-resolution
two- and three-nucleon interactions that predict realistic saturation
properties of nuclear matter. We focus on estimating the theoretical
uncertainties due to variation of the resolution scale, the low-energy
couplings, as well as from the many-body method. The experimental two-neutron
and two-proton separation energies are reasonably well reproduced, with an
uncertainty range of about 5 MeV. The first excited 2+ energies also show
overall agreement, with a more narrow uncertainty range of about 500 keV. In
most cases, this range is dominated by the uncertainties in the Hamiltonian.Comment: 6 pages, 4 figure
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