Photon production from non-equilibrium QGP in heavy ion collisions
  We present a calculation of thermal photon production i.e. photons from secondary interactions among particles produced in heavy ion collisions at collider energies. This is done within the framework of hydrodynamics. We take into account the lack of chemical equilibrium in QGP. It turns out that main effects from chemical non-equilibrium composition of QGP, reduction of particle number and increase in temperature, nearly cancel in photon spectrum. 
F. Gelis, H. Niemi, P. V. Ruuskanen and S. S. Rasanen