Event-by-event direct photon anisotropic flow in relativistic heavy-ion   collisions
  We consider directly emitted and hadronic decay photons from event-by-event hydrodynamic simulations. We compute the direct photon anisotropic flow coefficients and compare with recent experimental measurements. We find that it is crucial to include the photon multiplicity as a weighting factor in the definition of $v^\gamma_n$. We also investigate the sensitivity of the direct photon spectrum and elliptic flow to the theoretical uncertainty of the photon emission rate in the quark-hadron transition region and to the pre-equilibrium dynamics of relativistic heavy-ion collisions. 
Chun Shen, Jean-Francois Paquet, Jia Liu, Gabriel Denicol, Ulrich   Heinz, Charles Gale
nucl-th hep-ph nucl-ex