Two-pion exchange and strong form factors in covariant field theories - art. no. 047001

We evaluated box and crossed-box two-pion exchange diagrams. We found that form factors can induce contributions that violate the unitary cut requirem ent, and that the sum of subtracted and crossed-box amplitudes depends cruc ially on the meson-nucleon vertex functions. With form factors preserving t he unitarity condition, this sum can be made, at low energies, of the order of one heavy boson exchange, supporting the idea that it may be effectivel y represented by such types of terms. [S0556-2813(99)00409-4].