Relativistic theory of the evolution of nucleon structure in nuclei

The experimental and theoretical studies of lepton deep-inelastic scattering on nuclear targets are reviewed. The main problems which must be solved in analyzing the x and A dependences of the deep-inelastic cross sections are outlined. Several of the models proposed for studying the contribution of nuclear effects to the structure functions F2(x) are analyzed. A relativistic field-theoretical approach to studying lepton deep-inelastic scattering on very light nuclei is developed. The modifications of the nucleon structure in D, 3H 3He, and 4He are studied for the first time within a unified approach. It is found that the modifications evolve in a manner completely different from that observed earlier for heavy nuclei. In particular, it is found that the pattern of F2(x) modifications represented in terms of the ratios F^(2)lF^N(D)(2) is determined by the values (1 -X3)=0.32 (D/N), 0.16 (3He/D), and 0.08 (4He/D). These results allow the definition of the class of modifications of the bound-nucleon structure and the introduction of the unit of nucleon-structure modification. Theoretical justification of the concept of twostage evolution of the nucleon structure as a function of A, the first stage occurring for A<- 4 and the second for A>4, is also obtained. The long-standing problem of the nature of the EMC effect is explained as a modification of the nucleon structure in the field of the nuclear forces in a three-nucleon bound system.