Quantum Dynamics of the Slow Rollover Transition in the Linear Delta   Expansion
  We apply the linear delta expansion to the quantum mechanical version of the slow rollover transition which is an important feature of inflationary models of the early universe. The method, which goes beyond the Gaussian approximation, gives results which stay close to the exact solution for longer than previous methods. It provides a promising basis for extension to a full field theoretic treatment. 
H. F. Jones, P.Parkin and D. Winder