2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/21045The roton in a Bose-Einstein condensate is computed, both near and far from a Feshbach resonance. A low-density approximation is made, allowing for an analytic result. A Monte Carlo calculation shows that the roton is larger than predicted by the low-density approximation, for the upper range of densities considered here. The low-density approximation is applied to superfluid 4He, roughly reproducing the results of previous Monte Carlo calculations.This version has an improved pair functionSoft Condensed Mattertext