scholarly journals Low-Density Neutron Matter and the Unitary Limit

2021 ◽  
Vol 9 ◽  
Author(s):  
Isaac Vidaña
Keyword(s):  
Quantum Monte Carlo ◽  
Cold Atoms ◽  
Scattering Length ◽  
Fermi Gas ◽  
Neutron Matter ◽  
Bcs Theory ◽  
Unitary Limit ◽  
Strong Coupling Regime ◽  
Low Density ◽  
Contact Parameter

We review the properties of neutron matter in the low-density regime. In particular, we revise its ground state energy and the superfluid neutron pairing gap and analyze their evolution from the weak to the strong coupling regime. The calculations of the energy and the pairing gap are performed, respectively, within the Brueckner–Hartree–Fock (BHF) approach of nuclear matter and the Bardeen–Cooper–Schrieffer (BCS) theory using the chiral nucleon-nucleon interaction of Entem and Machleidt at N3LO and the Argonne V18 phenomenological potential. Results for the energy are also shown for a simple Gaussian potential with a strength and range adjusted to reproduce the 1S0 neutron-neutron scattering length and effective range. Our results are compared with those of quantum Monte Carlo (QMC) calculations for neutron matter and cold atoms. The Tan contact parameter in neutron matter is also calculated, finding a reasonable agreement with experimental data from ultra-cold atoms only at very low densities. We find that low-density neutron matter exhibits a behavior close to that of a Fermi gas at the unitary limit, although, this limit is actually never reached. We also review the properties (energy, effective mass, and quasiparticle residue) of a spin-down neutron impurity immersed in a low-density free Fermi gas of spin-up neutrons already studied by the author in a recent work where it was shown that these properties are very close to those of an attractive Fermi polaron in the unitary limit.

Equation of State and Pairing Gaps in Cold Atoms and Low-Density Neutron Matter

2008 ◽  
Author(s):  
J. Carlson ◽  
Alexandros Gezerlis ◽  
Sanjay Reddy ◽  
Pawel Danielewicz ◽  
Piotr Piecuch ◽  
...  
Keyword(s):  
Equation Of State ◽  
Cold Atoms ◽  
Neutron Matter ◽  
Low Density

scholarly journals A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential

2021 ◽  
Author(s):  
Subhanka Mal ◽  
Bimalendu Deb
Keyword(s):  
Quantum Monte Carlo ◽  
Chemical Potential ◽  
Scattering Length ◽  
Mean Field Theory ◽  
Mean Field ◽  
Fermi Gas ◽  
Range Limit ◽  
Contact Potential ◽  
Zero Range ◽  
Unitary Fermi Gas

Abstract We calculate Bardeen-Cooper-Schrieffer (BCS) state of a unitary Fermi gas of atoms interacting with the finite-ranged Jost-Kohn potential which has been recently shown to account for the resonant interactions [2019 {\rm J. Phys. B: At. Mol. Opt. Phys.} {\bf 52}, 165004]. Using exact scattering solution of the potential, we derive two-body ${\mathbf T}$-matrix element which is employed to construct the BCS Hamiltonian in momentum space. We present results on the energy- and range-dependence of the pairing gap and superfluid density and the range-dependence of the chemical potential for a wide variation of the scattering length including the \textcolor{red}{unitary} regime. In the zero range limit our calculated gap at the Fermi energy is found to be nearly equal to that calculated \textcolor{red}{in mean-field theory with contact potential}. The mean gap averaged over the full width at half maximum of the gap function in the zero range and unitary limits is found to be $0.42 E_F$ which is quite close to the recent result of the quantum Monte Carlo simulation [2018 {\rm Phys. Rev.A} {\bf 97}, 013601]. The chemical potential in the zero range limit also agrees well with that for the contact potential.

scholarly journals BCS-BEC Crossover Effects and Pseudogap in Neutron Matter

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 208
Author(s):  
David Durel ◽  
Michael Urban
Keyword(s):  
Matrix Theory ◽  
Scattering Length ◽  
Einstein Condensate ◽  
Neutron Matter ◽  
Strong Coupling Regime ◽  
Range Interaction ◽  
Bose Einstein Condensate ◽  
Crossover Effects ◽  
Weakly Coupled ◽  
Unitary Fermi Gas

Due to the large neutron–neutron scattering length, dilute neutron matter resembles the unitary Fermi gas, which lies half-way in the crossover from the BCS phase of weakly coupled Cooper pairs to the Bose–Einstein condensate of dimers. We discuss crossover effects in analogy with the T-matrix theory used in the physics of ultracold atoms, which we generalize to the case of a non-separable finite-range interaction. A problem of the standard Nozières–Schmitt-Rink approach and different ways to solve it are discussed. It is shown that in the strong-coupling regime, the spectral function exhibits a pseudo-gap at temperatures above the critical temperature Tc. The effect of the correlated density on the density dependence of Tc is found to be rather weak, but a possibly important effect due to the reduced quasiparticle weight is identified.

scholarly journals Ferromagnetism in the upper branch of the Feshbach resonance and the hard-sphere Fermi gas

2010 ◽  
Vol 108 (1) ◽  
pp. 51-54 ◽  
Author(s):  
Soon-Yong Chang ◽  
Mohit Randeria ◽  
Nandini Trivedi
Keyword(s):  
Quantum Monte Carlo ◽  
Hard Sphere ◽  
Feshbach Resonance ◽  
Scattering Length ◽  
Mean Field ◽  
Fermi Gas ◽  
Fundamental Interest ◽  
Pair Correlations ◽  
Total Energies ◽  
Quantum Monte Carlo Simulations

We address the question of ferromagnetism in repulsive Fermi gas, a problem of fundamental interest, using quantum Monte Carlo simulations that include backflow corrections. We investigate a two-component Fermi gas on the upper branch of a Feshbach resonance and contrast it with the hard-sphere gas. We find that, in both cases, the Fermi liquid becomes unstable to ferromagnetism at a kFa smaller than the mean field result, where kF is the Fermi wavevector and a is the scattering length. Even though the total energies E(kFa) are similar in the two cases, their pair correlations and kinetic energies are completely different, reflecting the underlying potentials. We discuss the extent to which our calculations shed light on recent experiments.

scholarly journals Next-to-next-to-leading-orderϵexpansion for a Fermi gas at infinite scattering length

2007 ◽  
Vol 75 (4) ◽  
Author(s):  
Peter Arnold ◽  
Joaquín E. Drut ◽  
Dam Thanh Son
Keyword(s):  
Scattering Length ◽  
Fermi Gas

scholarly journals Quantum Monte Carlo calculations of neutron matter

2003 ◽  
Vol 68 (2) ◽  
Author(s):  
J. Carlson ◽  
J. Morales ◽  
V. R. Pandharipande ◽  
D. G. Ravenhall
Keyword(s):  
Monte Carlo ◽  
Quantum Monte Carlo ◽  
Neutron Matter ◽  
Monte Carlo Calculations
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