Speaker: Yang Ma
Similar to the quark and gluon partons in quantum chromodynamics, photon could be treated as a parton constituent in the initial state beam particles and described using a photon parton distribution function (PDF). This ``equivalent photon approximation'' is a powerful tool both in understanding the electromagnetic radiation and in studying the photon interaction processes. However, questions arise when people consider physics processes beyond the electroweak (EW) scale characterized by Z boson mass m_Z, where the ``photon'' is not well defined any more. Does the conventional photon PDF remain valid at scales above mZ ? Do we need to consider adding in the Z and the photon-Z mixing PDFs to count the interference? How much do the EW PDFs affect the theoretical predictions? I will try to show the full picture of the EW PDFs and talk about the new features that we would see on a possible high energy lepton collider.