  A theory of superconductivity based on the two-body Cooperon propagator is
presented. This theory takes the form of a modified Gorkov equation for the
Green's function and allows one to model the effect of local superconducting
correlations and long range phase fluctuations on the spectral properties of
high temperature superconductors, both above and below Tc. A model is proposed
for the Cooperon propagator, which provides a simple physical picture of the
pseudo-gap phenomenon, as well as new insights into the doping dependence of
the spectral properties. Numerical calculations of the density of states and
spectral functions based on this model are also presented, and compared with
the experimental STM and ARPES data. It is found, in particular, that the
sharpness of the peaks in the density of states is related to the strength and
the range of the superconducting correlations and that the apparent pseudo-gap
in STM and ARPES can be different, although the underlying model is the same.
