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-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'NN) and (\gamma, NN) reactions where the two--body overlap functions are a key ingredient in the analysis.