Analytical results for a trapped, weakly-interacting Bose-Einstein   condensate under rotation
  We examine the problem of a repulsive, weakly-interacting and harmonically trapped Bose-Einstein condensate under rotation. We derive a simple analytic expression for the energy incorporating the interactions when the angular momentum per particle is between zero and one and find that the interaction energy decreases linearly as a function of the angular momentum in agreement with previous numerical and limiting analytical studies. 
A. D. Jackson (Niels Bohr Institute, Denmark) and G. M. Kavoulakis   (NORDITA, Denmark)