Multicomponent Fermi systems at low densities

TL;DR

This paper calculates the quasiparticle interactions in low-density, multicomponent Fermi systems, extending previous results and revealing a novel energy density dependence for low proton concentrations relevant to nuclear physics.

Contribution

It provides a second-order calculation of Landau quasiparticle interactions in multicomponent Fermi systems with unequal densities, including a new low-concentration energy density behavior.

Findings

Agreement with Kanno's earlier results.

Derived energy density dependence as x^{7/3} log x for low proton concentrations.

Extended analysis to nuclear matter with neutrons and protons.

Abstract

We calculate, to second order in the scattering length between two fermions, the Landau quasiparticle interaction for a low-density mixture of two fermion species with unequal densities at temperature zero. From the Landau parameters we evaluate the energy density and find agreement with the result of Kanno, Prog. Theor. Phys. 44, 813 (1970). The calculations are then extended to the case of two fermion components with different total densities, each with two spin components, a situation of interest in nuclear physics and astrophysics, where the species are neutrons and protons. An interesting finding is that, for low proton concentrations, $x \ll 1$, the leading term in the energy density, beyond the $x^{5/3}$ contribution from the kinetic energy and the $x^2$ one due to the two-body interaction in the mean-field approximation, varies as $x^{7/3} \ln x$. This is to be contrasted with the higher powers of $x$ implicit in many phenomenological energy-density functionals employed in nuclear physics, such as those of the Skyrme type.