Photon parton distributions in nuclei and the EMC effect

Understand

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 \propto \alpha_{em}(Z^2/A^{4/3})\ln(1/R_{A}m_{N}x) to the nuclear structure functions as well as the term \propto \alpha_{em}Z/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.