A consistent approximation scheme beyond RPA for bosons
  In this paper, we develop a consistent extension of RPA for bosonic systems. In order to illustrate the method, we consider the case of the anharmonic oscillator. We compare our results with those obtained in mean-field and standard RPA approaches, with the exact ones and show that they are very close to the exact ones. 
D. Davesne, M. Oertel, H. Hansen (Institut de Physique Nucleaire de   Lyon, France)