Exact Eigenstates for Repulsive Bosons in Two Dimensions
  We consider a model of $N$ two-dimensional bosons in a harmonic potential with weak repulsive delta-function interactions. We show analytically that, for angular momentum $L\le N$, the elementary symmetric polynomials of particle coordinates measured from the center of mass are exact eigenstates with energy $N(N-L/2-1)$. Extensive numerical analysis confirms that these are actually the ground states, but we are currently unable to prove this analytically. The special case $L=N$ can be thought of as the generalisation of the usual superfluid one-vortex state to Bose-Einstein condensates in a trap. 
R A Smith and N K Wilkin (University of Birmingham, England)