Excitation spectrum of Bose gases beyond the Gross–Pitaevskii regime

Abstract

We consider Bose gases of [Formula: see text] particles in a box of volume one, interacting through a repulsive potential with scattering length of order [Formula: see text], for [Formula: see text]. Such regimes interpolate between the Gross–Pitaevskii and thermodynamic limits. Assuming that [Formula: see text] is sufficiently small, we determine the ground state energy and the low-energy excitation spectrum, up to errors vanishing in the limit [Formula: see text].