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ABSTRACT: We calculate properties of neutron drops in external potentials using both
quantum Monte Carlo and no-core full configuration techniques. The properties
of the external wells are varied to examine different density profiles. We
compare neutron drop results given by a selection of nuclear Hamiltonians,
including realistic two-body interactions as well as several three-body forces.
We compute a range of properties for the neutron drops: ground-state energies,
spin-orbit splittings, excitation energies, radial densities and rms radii. We
compare the equations of state for neutron matter for several of these
Hamiltonians. Our results can be used as benchmarks to test other many-body
techniques, and to constrain properties of energy-density functionals.
02/2013;
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ABSTRACT: Background: The calculation of the hyperon binding energy in hypernuclei is
crucial to understanding the interaction between hyperons and nucleons.
Purpose: We assess the relative importance of two- and three-body
hyperon-nucleon force by studying the effect of the hyperon-nucleon-nucleon
interaction in closed shell \Lambda-hypernuclei from A=5 to 91.
Methods: The \Lambda-binding energy has been calculated using the auxiliary
field diffusion Monte Carlo method for the first time, to study light and heavy
hypernuclei within the same model.
Results: Our results show that including a three-body component in the
hyperon-nucleon interaction leads to a saturation of the \Lambda-binding energy
remarkably close to the experimental data. In contrast, the two-body force
alone gives an unphysical limit for the binding energy.
Conclusions: The repulsive contribution of the three-body
hyperon-nucleon-nucleon force is essential to reproduce, even qualitatively,
the binding energy of the hypernuclei in the mass range considered.
01/2013;
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ABSTRACT: We investigate the role of two- and three-body $\Lambda$-nucleon forces by
computing the ground state of a few $\Lambda$-hypernuclei with the Auxiliary
Field Diffusion Monte Carlo algorithm. Calculations have been performed for
masses up to A=41, including some open-shell hypernuclei. The results show that
the use of a bare hyperon-nucleon force fitted on the available scattering data
yields a consistent overestimate of the $\Lambda$-separation energy
$B_\Lambda$. The inclusion of a hyperon-nucleon-nucleon interaction
systematically reduces $B_\Lambda$, leading to a qualitatively good agreement
with experimental data over the range of masses investigated.
11/2012;
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ABSTRACT: 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.
04/2012;
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ABSTRACT: 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.
Physical Review Letters 01/2011; 106(1):012501. · 7.37 Impact Factor
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ABSTRACT: The contact parameter in unitary Fermi Gases governs the short-distance,
high-momentum, and high-energy properties of the system. We perform accurate
quantum Monte Carlo calculations with highly optimized trial functions to
precisely determine this parameter at T=0, demonstrate its universal
application to a variety of observables, and determine the regions of momentum
and energy over which the leading short-range behavior is dominant. We derive
Tan's expressions for the contact parameter using just the short-range behavior
of the ground-state many-body wave function, and use this behavior to calculate
the two-body distribution function, one-body density matrix, and the momentum
distribution of unitary Fermi gases; providing a precise value of the contact
parameter that can be compared to experiments.
12/2010;
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ABSTRACT: We present results for neutron star models constructed with a new equation of state for nuclear matter at zero temperature. The ground state is computed using the Auxiliary Field Diffusion Monte Carlo (AFDMC) technique, with nucleons interacting via a semi-phenomenological Hamiltonian including a realistic two-body interaction. The effect of many-body forces is included by means of additional density-dependent terms in the Hamiltonian. In this letter we compare the properties of the resulting neutron-star models with those obtained using other nuclear Hamiltonians, focusing on the relations between mass and radius, and between the gravitational mass and the baryon number. Comment: modified version with a slightly different Hamiltonian and parametrization of the EOS
09/2009;
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ABSTRACT: We investigate fermion pairing in the unitary regime for a mass ratio corresponding to a ;{6}Li-;{40}K mixture using quantum Monte Carlo methods. The ground-state energy and the average light- and heavy-particle excitation spectrum for the unpolarized superfluid state are nearly independent of the mass ratio. In the majority light system, the polarized superfluid is close to the energy of a phase separated mixture of nearly fully polarized normal and unpolarized superfluid. For a majority of heavy particles, we find an energy minimum for a normal state with a ratio of approximately 3ratio1 heavy to light particles. A slight increase in attraction to k_{F}a approximately 2.5 yields a ground state energy of nearly zero for this ratio. A cold unpolarized system in a harmonic trap at unitarity should phase separate into three regions, with a shell of unpolarized superfluid in the middle.
Physical Review Letters 08/2009; 103(6):060403. · 7.37 Impact Factor
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ABSTRACT: We report results of the equation of state of neutron matter in the low--density regime, where the Fermi wave vector ranges from $0.4 fm^{-1} \leq k_F \leq 1.0 fm^{-1}$. Neutron matter in this regime is superfluid because of the strong and attractive interaction in the $^1S_0$ channel. The properties of this superfluid matter are calculated starting from a realistic Hamiltonian that contains modern two-- and three--body interactions. The ground state energy and the $^1S_0$ superfluid energy gap are calculated using the Auxiliary Field Diffusion Monte Carlo method. We study the structure of the ground state by looking at pair distribution functions as well as the Cooper-pair wave function used in the calculations. Comment: 12 pages, 7 figures
07/2009;
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ABSTRACT: We present a novel technique well suited for studying the ground state of inhomogeneous fermionic matter in a wide range of different systems. The system is described using a fermionic shadow wave function, and the energy is computed by means of the variational Monte Carlo technique. The general form of the fermionic shadow wave function is useful for describing many-body systems with the coexistence of different phases as well in the presence of defects or impurities, but it requires overcoming a significant sign problem. As an application, we studied the energy to activate vacancies in solid 3He.
Physical Review Letters 07/2009; 102(25):255302. · 7.37 Impact Factor
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ABSTRACT: We present a novel technique well suited to study the ground state of inhomogeneous fermionic matter in a wide range of different systems. The system is described using a Fermionic Shadow wavefunction (FSWF) and the energy is computed by means of the Variational Monte Carlo technique. The general form of FSWF is useful to describe many--body systems with the coexistence of different phases as well in the presence of defects or impurities, but it requires overcoming a significant sign problem. As an application, we studied the energy to activate vacancies in solid $^3$He. Comment: 4 pages, 2 figures
06/2009;
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ABSTRACT: We calculate the equation of state of neutron matter at zero temperature by means of the auxiliary field diffusion Monte Carlo method (AFDMC) combined with a fixed-phase approximation. The calculation of the energy is carried out by simulating up to 114 neutrons in a periodic box. Special attention was made to reduce finite size effects at the energy evaluation by adding to the interaction the effect due to the truncation of the simulation box, and by performing several simulations using different number of neutrons. The finite size effects due to the kinetic energy were also checked by employing the twist--averaged boundary conditions. We considered a realistic nuclear Hamiltonian containing modern two-- and three--body interactions of the Argonne and Urbana family. The equation of state can be used to compare and to calibrate other many-body calculations and to predict properties of neutron stars.
03/2009;
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ABSTRACT: We present a quantum Monte Carlo study of the zero-temperature equation of state of neutron matter and the computation of the 1S0 pairing gap in the low-density regime with rho < 0.04 fm(-3). The system is described by a nonrelativistic 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.
Physical Review Letters 09/2008; 101(13):132501. · 7.37 Impact Factor
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ABSTRACT: We computed ground-state energies of calcium isotopes from 42Ca to 48Ca by means of the Auxiliary Field Diffusion Monte Carlo (AFDMC) method. Calculations were performed by replacing the 40Ca core with a mean-field self-consistent potential computed using the Skyrme interaction. The energy of the external neutrons
is calculated by projecting the ground state from a wave function built with the single-particle orbitals computed in the
self-consistent external potential. The shells considered were the 1F
7/2 and the 1F
5/2 . The Hamiltonian employed is semi-realistic and includes tensor, spin-orbit and three-body forces. While absolute binding
energies are too deep if compared with experimental data, the differences between the energies for nearly all isotopes are
in very good agreement with the experimental data.
European Physical Journal A 01/2008; 35(2):207-211. · 2.19 Impact Factor
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ABSTRACT: We calculate the ground-state energy of (4)He, (8)He, (16)O, and (40)Ca using the auxiliary field diffusion Monte Carlo method in the fixed-phase approximation and the Argonne v(6)' interaction which includes a tensor force. Comparison of our light nuclei results to those of Green's function Monte Carlo calculations shows the accuracy of our method for both open and closed-shell nuclei. We also apply it to (16)O and (40)Ca to show that quantum Monte Carlo methods are now applicable to larger nuclei.
Physical Review Letters 08/2007; 99(2):022507. · 7.37 Impact Factor
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ABSTRACT: We present an accurate numerical study of the equation of state of nuclear matter based on realistic nucleon--nucleon interactions by means of Auxiliary Field Diffusion Monte Carlo (AFDMC) calculations. The AFDMC method samples the spin and isospin degrees of freedom allowing for quantum simulations of large nucleonic systems and represents an important step forward towards a quantitative understanding of problems in nuclear structure and astrophysics.
12/2006;
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ABSTRACT: We computed ground-state energies of calcium isotopes from 42Ca to 48Ca by means of the Auxiliary Field Diffusion Monte Carlo (AFDMC) method. Calculations were performed by replacing the 40Ca core with a mean-field self consistent potential computed using Skyrme interaction. The energy of the external neutrons is calculated by projecting the ground-state from a wave function built with the single particle orbitals computed in the self consistent external potential. The shells considered were the 1F_7/2 and the 1F_5/2. The Hamiltonian employed is semi-realistic and includes tensor, spin--orbit and three--body forces. While absolute binding energies are too deep if compared with experimental data, the differences between the energies for nearly all isotopes are in very good agreement with the experimental data.
06/2006;
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ABSTRACT: The ground state and some low-lying excited states of oxygen isotopes 18O–22O were simulated by means of auxiliary field diffusion Monte Carlo techniques. We performed the calculations by replacing the 16O core with a mean-field self-consistent potential we computed by using Skyrme interactions. The external neutrons were included in the Monte Carlo calculations, building a wave function with the orbitals computed in the self-consistent external potential. The shell considered was the 1D5/2. The NN interactions employed included tensor, spin-orbit, and three-body forces. While absolute binding energies are too deep compared with those of experimental data, the differences between the energies for nearly all isotopes and excitations are in very good agreement with the experiments. The exception is the 4+ state of the 18O isotope, which shows a larger discrepancy.
Phys. Rev. C. 04/2006; 73(4).
