  We investigate the two-dimensional cooperon-fermion model in the correlated
regime with a new continuous-time diagrammatic determinant quantum Monte Carlo
(DDQMC) algorithm. We estimate the transition temperature $T_{c}$, examine the
effectively reduced band gap and cooperon mass, and find that delocalization of
the cooperons enhances the diamagnetism. When applied to diamagnetism of the
pseudogap phase in high-$T_{c}$ cuprates, we obtain results in a qualitative
agreement with recent torque magnetization measurements.
