Fermi polaron in low-density spin-polarized neutron matter

I study the properties of a spin-down neutron impurity immersed in a low-density free Fermi gas of spin-up neutrons. In particular, I analyze its energy (E-down arrow), effective mass (m(down arrow)*), and quasiparticle residue (Z(down arrow)). Results are compared with those of state-of-the-art quantum Monte Carlo calculations of the attractive Fermi polaron realized in ultracold atomic gases experiments, and with those of previous studies of the neutron polaron. Calculations are performed within the Brueckner-Hartree-Fock approach using the chiral two-body nucleon-nucleon interaction of Entem and Machleidt at (NLO)-L-3 with a 500 MeV cut-off and the Argonne V18 phenomenological potential. Only contributions from the S-1(0) partial wave, which is the dominant one in the low-density region considered, are included. Contributions from three-nucleon forces are expected to be irrelevant at these densities and, therefore, are neglected in the calculation. It is shown that for Fermi momenta between approximate to 0.25 and approximate to 0.45 fm(-1) the energy, effective mass, and quasiparticle residue of the impurity vary only slightly, respectively, in the ranges -0.604 E-F < E-down arrow < -0.635 E-F, 1.300 m(down arrow)* < any< 1.085 m, and 0.741 < Z(down arrow) < 0.836 in the case of the chiral interaction, and -0.621 E-F < E-down arrow < -0.643 E-F, 1.310 m(down arrow*) < any< 1.089 m, and 0.739 < Z(down arrow)< 0.832 when using the Argonne V18 potential. These results are compatible with those derived from ultracold atoms and show that a spin-down neutron impurity in a free Fermi gas of spin-up neutrons with a Fermi momentum in the range 0.25 less than or similar to k(F) less than or similar to 0.45 fm(-1) exhibits properties very similar to those of an attractive Fermi polaron in the unitary limit.