Photon parton distributions in nuclei and the EMC effect

Photons, as well as quarks and gluons, are constituents of the infinite momentum frame (IMF) wave function of an energetic particle. They are mostly equivalent photons whose amplitude follows from the Lorentz transformation of the particle rest frame Coulomb field into the IMF and from the conservation of the electromagnetic current. We evaluate in a model independent way the dominant photon contribution α_em(Z2/A4⊃/3)ln(1/R_Am _Nx) to the nuclear structure functions as well as the term α_emZ/A. In addition we show that the definition of x consistent with the exact kinematics of eA scattering (with exact sum rules) works in the same direction as the nucleus field of equivalent photons. Combined, these effects account for the bulk of the hadronic European Muon Collaboration (EMC) effect for x≤0.5 where Fermi motion effects are small. In particular, for these x the hadronic mechanism contribution to the EMC effect does not exceed ∼3% for all nuclei. Also, the A dependence of the hadronic mechanism of the EMC effect for x>0.5 is significantly modified.