Relationships between two-particle overlap functions and the two-body density matrix for many-fermion systems.

Relationships are obtained connecting the two-nucleon overlap function of the eigenstates in the $(A\ensuremath{-}2)$ particle system with the asymptotic behavior of the two-body density matrix for the ground state of the A-particle system. This makes it possible to calculate the two-body overlap functions, spectroscopic factors and separation energies on the basis of a realistic two-body density matrix. The procedure can be used in describing the ${(e,e}^{\ensuremath{'}}NN)$ and $(\ensuremath{\gamma},NN)$ reactions where the two-body overlap functions are a key ingredient in the analysis.