2,080 research outputs found
Superfluid Pairing in Neutrons and Cold Atoms
Ultracold atomic gases and low-density neutron matter are unique in that they
exhibit pairing gaps comparable to the Fermi energy which in this sense are the
largest in the laboratory and in nature, respectively. This strong pairing
regime, or the crossover between BCS and BEC regimes, requires non-perturbative
treatments. We describe Quantum Monte Carlo results useful to understand the
properties of these systems, including infinite homogeneous matter and trapped
inhomogeneous gases.Comment: 14 pages, 4 figures; chapter in "50 Years of Nuclear BCS", edited by
R. A. Broglia and V. Zelevinsk
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
Contact interaction in an unitary ultracold Fermi gas
An ultracold Fermi atomic gas at unitarity presents universal properties that
in the diluted limit can be well described by a contact interaction. By
employing a guide function with correct boundary conditions and making simple
modifications to the sampling procedure we are able to handle for the first
time a true contact interaction in a quantum Monte Carlo calculation. The
results are obtained with small variances. Our calculations for the Bertsch and
contact parameters are in excellent agreement with published experiments. The
possibility of using a more faithfully description of ultracold atomic gases
can help uncover features yet unknown of the ultracold atomic gases. In
addition, this work paves the way to perform quantum Monte Carlo calculations
for systems interacting with contact interactions, where in many cases the
description using potentials with finite effective range might not be accurate
The equation of state of neutron matter, symmetry energy, and neutron star structure
We review the calculation of the equation of state of pure neutron matter
using quantum Monte Carlo (QMC) methods. QMC algorithms permit the study of
many-body nuclear systems using realistic two- and three-body forces in a
nonperturbative framework. We present the results for the equation of state of
neutron matter, and focus on the role of three-neutron forces at supranuclear
density. We discuss the correlation between the symmetry energy, the neutron
star radius and the symmetry energy. We also combine QMC and theoretical models
of the three-nucleon interactions, and recent neutron star observations to
constrain the value of the symmetry energy and its density dependence.Comment: 11 pages, 11 figure
Equation of state of superfluid neutron matter and the calculation of pairing gap
We present a Quantum Monte Carlo study of the zero temperature equation of
state of neutron matter and the computation of the pairing gap in the
low-density regime with fm. The system is described by a
non-relativistic nuclear Hamiltonian including both two-- and three--nucleon
interactions of the Argonne and Urbana type. This model interaction provides
very accurate results in the calculation of the binding energy of light nuclei.
A suppression of the gap with respect to the pure BCS theory is found, but
sensibly weaker than in other works that attempt to include polarization
effects in an approximate way
Quantum Monte Carlo Calculations of Light Nuclei Using Chiral Potentials
We present the first Green's function Monte Carlo calculations of light
nuclei with nuclear interactions derived from chiral effective field theory up
to next-to-next-to-leading order. Up to this order, the interactions can be
constructed in a local form and are therefore amenable to quantum Monte Carlo
calculations. We demonstrate a systematic improvement with each order for the
binding energies of and systems. We also carry out the first
few-body tests to study perturbative expansions of chiral potentials at
different orders, finding that higher-order corrections are more perturbative
for softer interactions. Our results confirm the necessity of a three-body
force for correct reproduction of experimental binding energies and radii, and
pave the way for studying few- and many-nucleon systems using quantum Monte
Carlo methods with chiral interactions.Comment: 5 pages, 3 figures, 4 tables. Updated references. Cosmetic changes to
figures, tables, and equations; added a sentence clarifying the
correspondence between our real-space cutoffs and momentum-space cutoffs.
Other sentences were reworded for clarit
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