Structure Functions of the Nucleon in a Covariant Scalar Spectator Model
  Nucleon structure functions, as measured in deep-inelastic lepton scattering, are studied within a covariant scalar diquark spectator model. Regarding the nucleon as an approximate two-body bound state of a quark and diquark, the Bethe-Salpeter equation (BSE) for the bound state vertex function is solved in the ladder approximation. The valence quark distribution is discussed in terms of the solutions of the BSE. 
K. Kusaka, G. Piller, A.W. Thomas and A.G. Williams