Two-body scattering states in Minkowski space and the Nakanishi integral   representation onto the null plane
  The Nakanishi perturbative integral representation of the four-dimensional T-matrix is investigated in order to get a workable treatment for scattering states, solutions of the inhomogeneous Bethe-Salpeter Equation, in Minkowski space. The projection onto the null-plane of the four-dimensional inhomogeneous Bethe-Salpeter Equation plays a key role for devising an equation for the Nakanishi weight function (a real function), as in the homogeneous case that corresponds to bound states and it has been already studied within different frameworks. In this paper, the whole formal development is illustrated in detail and applied to a system, composed by two massive scalars interacting through the exchange of a massive scalar. The explicit expression of the scattering integral equations are also obtained in ladder approximation, and, as simple applications of our formalism, some limiting cases, like the zero-energy limit and the Wick-Cutkosky model in the continuum, are presented. 
Tobias Frederico (CTA-S\~ao Jos\'e dos Campos), Giovanni Salm\`e   (INFN-Rome), Michele Viviani (INFN - Pisa)
hep-ph cond-mat.soft cond-mat.str-el nucl-th