An improvement on RPA based on a Boson mapping
  We use a solvable model to perform modified dyson mapping and reveal the unphysical-state effects in the original Random Phase Approximation (RPA). We then propose a method to introduce the RPA and improve it based on a Boson mapping. 
Shi-Lin Zhu, Zhi-ning Zhou and Ze-sen Yang, (Physics Department,   Peking University)