Perturbation theory in a correlated basis

Abstract

We give a brief outline of correlated basis functions (CBF) theory focusing the discussion on the linked cluster property of the theory, the diagrammatical rules of the perturbative series and its similarities with standard perturbation theory. Next, we discuss the choice of the correlation operator and give results obtained for the binding energy, the optical potential and the momentum distribution of nuclear matter by using variational theory plus second order CBF perturbation theory. When a state dependent pair correlation is used for the correlation operator, the second order perturbative corrections are generally small, nevertheless they are essential to reproduce important effects like the enhancement of the effective mass and the logarithmic slope of the momentum distribution at k=kF. The results obtained are compared with other theoretical estimates and with the available experimental data. The agreement with the empirical data is all over fairly good. Most of the discrepancies are attributed to the coupling of low lying states to surface vibrations, not present in infinite nuclear matter.