Low-lying excitations of a trapped rotating Bose-Einstein condensate
  We investigate the low-lying excitations of a weakly-interacting, harmonically-trapped Bose-Einstein condensed gas under rotation, in the limit where the angular mometum $L$ of the system is much less than the number of the atoms $N$ in the trap. We show that in the asymptotic limit $N \to \infty$ the excitation energy, measured from the energy of the lowest state, is given by $27 N_{3}(N_{3}-1) v_0 /68$, where $N_{3}$ is the number of octupole excitations and $v_{0}$ is the unit of the interaction energy. 
G. M. Kavoulakis (Royal Institute of Technology, Sweden), B. Mottelson   (NORDITA, Denmark), and S. M. Reimann (University o...