Recent developments of the covariant Bethe-Salpeter (BS) approach with the use of the separable interaction for the deuteron are reviewed. It is shown that the BS formalism allows a covariant description of various electromagnetic reactions like the lepton-deuteron scattering, deuteron electro-disintegration, deep inelastic scattering (DIS) of leptons on light nuclei. The procedure of the construction of the separable nucleon-nucleon (N N ) interaction is discussed. The BS formalism facilitates analysis of the role of the P -waves (negative energy components) in the electromagnetic properties of the deuteron and its comparison with the nonrelativistic results. Furthermore the covariant BS approach makes it possible to analyze DIS of leptons from the deuteron in a model independent way and to extend the formalism to DIS reactions on the light nuclei. Appendix A 82 Appendix B 83 ′ ′ ′

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We investigate the nonrelativistic reduction of the Bethe-Salpeter amplitude for the deuteron electrodisintegration near threshold energies. To this end, two assumptions have been used in the calculations: 1) the static approximation and 2) the one iteration approximation. Within these assumptions it is possible to recover the nonrelativistic result including a systematic extension to relativistic corrections. We find that the so-called pair current term can be constructed from the P -wave contribution of the deuteron Bethe-Salpeter amplitude. The form factor that enters into the calculation of the pair current is constrained by the manifestly gauge independent matrix elements.

The evolution of the nucleon structure as a function of atomic mass A is considered for the first time for the lightest nuclei, D, 3 H, 3 He and 4 He, with an approach based on the Bethe-Salpeter formalism. We show that the pattern of the oscillation of the structure functions ratio rvaries with A by changing the position of the crossover point x 3 in which r A (x) = 1, unlike the pattern for nuclei with masses A > 4, where only the amplitude of the oscillation changes. In particular we find that the pattern of F 2 (x) modifications is controlled with the values (1 − x 3 ) = 0.32 (D/N), 0.16 ( 3 He/D) and 0.08 ( 4 He/D). The obtained results follow from the relativistic consideration of the nuclear structure and allow us to define a whole class of modifications of the partonic distributions in the nucleon bound in a nucleus. The EMC effect is explained as a particular case of the considered class.