Effects of Longitudinal Photons
  The description of longitudinal photons is far from trivial, and their phenomenological importance is largely unknown. While the cross section for direct interactions is calculable, an even more important contribution could come from resolved states. In the development of our model for the interactions of (real and) virtual photons, we have modeled resolved longitudinal effects by simple multiplicative factors on the resolved transverse-photon contributions. Recently, a first set of parton distributions for longitudinal virtual photons has been presented by Ch\'yla. We therefore compare their impact on some representative distributions, relative to the simpler approaches. 
Christer Friberg and Torbj\"orn Sj\"ostrand (Lund university, Sweden)