Metastability of Bose and Fermi gases on the upper branch

TL;DR

This paper investigates the metastable upper branch phase of three-dimensional Bose and Fermi gases, deriving analytic expressions and phase diagrams within a two-body interaction approximation and S-matrix formalism.

Contribution

It provides the first analytic expressions and phase diagrams for Bose and Fermi gases on the upper branch considering arbitrary positive scattering lengths.

Findings

Derived analytic expressions for upper branch gases.

Established phase diagrams for bosons and fermions.

Validated techniques for weak coupling regimes.

Abstract

We study three dimensional Bose and Fermi gases in the upper branch, a phase defined by the absence of bound states in the repulsive interaction regime, within an approximation that considers only two-body interactions. Employing a formalism based on the S-matrix, we derive useful analytic expressions that hold on the upper branch in the weak coupling limit. We determine upper branch phase diagrams for both bosons and fermions with techniques valid for arbitrary positive scattering length.