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 these ones. Received: 17 June 2002 / Accepted: 14 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: davesne@ipnl.in2p3.fr Communicated by A. Molinari