2,924 research outputs found
Cold neutrons trapped in external fields
The properties of inhomogeneous neutron matter are crucial to the physics of
neutron-rich nuclei and the crust of neutron stars. Advances in computational
techniques now allow us to accurately determine the binding energies and
densities of many neutrons interacting via realistic microscopic interactions
and confined in external fields. We perform calculations for different external
fields and across several shells to place important constraints on
inhomogeneous neutron matter, and hence the large isospin limit of the nuclear
energy density functionals that are used to predict properties of heavy nuclei
and neutron star crusts. We find important differences between microscopic
calculations and current density functionals; in particular the isovector
gradient terms are significantly more repulsive than in traditional models, and
the spin-orbit and pairing forces are comparatively weaker.Comment: 5 pages, 4 figures, final version. Additional material reference
added in the published versio
Quantum Monte Carlo study of inhomogeneous neutron matter
We present an ab-initio study of neutron drops. We use Quantum Monte Carlo
techniques to calculate the energy up to 54 neutrons in different external
potentials, and we compare the results with Skyrme forces. We also calculate
the rms radii and radial densities, and we find that a re-adjustment of the
gradient term in Skyrme is needed in order to reproduce the properties of these
systems given by the ab-initio calculation. By using the ab-initio results for
neutron drops for close- and open-shell configurations, we suggest how to
improve Skyrme forces when dealing with systems with large isospin-asymmetries
like neutron-rich nuclei.Comment: 8 pages, 6 figures, talk given at Horizons on Innovative Theories,
Experiments, and Supercomputing in Nuclear Physics 2012, (HITES2012), New
Orleans, Louisiana, June 4-7, 2012; to appear in Journal of Physics:
Conference Series (JPCS
The equation of state of neutron star matter and the symmetry energy
We present an overview of microscopical calculations of the Equation of State
(EOS) of neutron matter performed using Quantum Monte Carlo techniques. We
focus to the role of the model of the three-neutron force in the high-density
part of the EOS up to a few times the saturation density. We also discuss the
interplay between the symmetry energy and the neutron star mass-radius
relation.
The combination of theoretical models of the EOS with recent neutron stars
observations permits us to constrain the value of the symmetry energy and its
slope. We show that astrophysical observations are starting to provide
important insights into the properties of neutron star matter.Comment: 7 pages, 3 figure, talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Recent Developments in the Nuclear Many-Body Problem
The study of quantum chromodynamics (QCD) over the past quarter century has
had relatively little impact on the traditional approach to the low-energy
nuclear many-body problem. Recent developments are changing this situation. New
experimental capabilities and theoretical approaches are opening windows into
the richness of many-body phenomena in QCD. A common theme is the use of
effective field theory (EFT) methods, which exploit the separation of scales in
physical systems. At low energies, effective field theory can explain how
existing phenomenology emerges from QCD and how to refine it systematically.
More generally, the application of EFT methods to many-body problems promises
insight into the analytic structure of observables, the identification of new
expansion parameters, and a consistent organization of many-body corrections,
with reliable error estimates.Comment: 15 pages, 10 figures, plenary talk at the 11th Conference on Recent
Progress in Many-Body Theories (MB 11), Manchester, England, 9-13 Jul 200
Neutron Drops and Skyrme Energy-Density Functionals
The J=0 ground state of a drop of 8 neutrons and the lowest
1/2 and 3/2 states of 7-neutron drops, all in an external well, are
computed accurately with variational and Green's function Monte Carlo methods
for a Hamiltonian containing the Argonne two-nucleon and Urbana IX
three-nucleon potentials. These states are also calculated using Skyrme-type
energy-density functionals. Commonly used functionals overestimate the central
density of these drops and the spin-orbit splitting of 7-neutron drops.
Improvements in the functionals are suggested
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