Third order corrections to the ground state energy of the gas of spin $s$ fermions with arbitrary densities of different spin projections

Abstract

Recently we have computed the third order corrections to the ground state energy of the arbitrarily polarized diluted gas of spin 1/2 fermions interacting through a spin-independent repulsive two-body potential. Here we extend this result to the gas of spin $s$ fermions - a system the Hamiltonian of which has an accidental $SU(2s+1)$ symmetry - with arbitrary densities of fermions having different spin projections. The corrections are computed semi-analytically using the effective field theory approach and are parametrized by the $s$- and $p$- wave scattering lengths $a_0$ and $a_1$ and the $s$-wave effective radius $r_0$, measurable in the low energy fermion-fermion elastic scattering. The result is used to study the impact the higher order corrections can have on the characteristics of the phase transition (at zero temperature) to the ordered phase (on the emergence of the itinerant ferromagnetism).