QED radiative corrections for parton distributions.

Abstract

I discuss radiative corrections due to the emission of photons from quarks which contribute to deep inelastic lepton--nucleon scattering as well as to $pp$ collisions at high energies. These corrections are dominated by quark-mass singularities which have to be absorbed into the parton distribution functions. Observable effects appear as a modification of the $Q^2$ dependence of the distribution functions. Numerical results indicate, however, that these QED corrections are negligible except at extremely large $Q^2$ and large $x$. Therefore it is safe to neglect the single and multiple photon effects in $pp$ scattering at LHC energies.