The relevance of $\gamma_L^*$ in hard collisions of virtual photons
  We explore the relevance of extending the concept of the structure to the longitudinally polarized virtual photon involved in hard collisions. We show that for moderate photon virtualities and in the kinematical region accessible in current experiments at HERA and LEP, the contributions of its longitudinal polarization to hard collisions are sizable and should be taken into account as part of the resolved photon component. 
Jiri Chyla and Marek Tasevsky