Recent Pythia 8 developments: Hard diffraction, Colour reconnection and   $\gamma\gamma$ collisions
  An overview of recent developments in \pythia~8 is given. First the new hard diffraction model, which is implemented as a part of the multiparton interactions (MPI) framework, is discussed. Then the new colour reconnection model, which includes beyond leading colour effects that can become important when MPI are present, is briefly reviewed. As a last topic an introduction is given to our implementation of photon-photon collisions. In particular photon PDFs, required modifications for the initial state radiation algorithm and beam remnant handling with photon beams is discussed. 
Ilkka Helenius, Jesper R. Christiansen and Christine O. Rasmussen
hep-ph