Abstract: Direct Photons in heavy-ion collisions from microscopic transport theory and fluid dynamics
Direct photon emission in heavy-ion collisions is calculated within the relativistic microscopic transport model UrQMD. We
compare the results from the pure transport calculation to a hybrid-model calculation, where the high-density part
of the evolution is replaced by an ideal 3D fluiddynamic calculation. The impact of different Equations
of State in the latter case is studied. Also, the effects of viscosity, present in the
transport model but neglected in ideal fluiddynamics, are examined.
We also study the contribution of different production channels and non-thermal collisions to the spectrum of
direct photons. Detailed comparison to the measurements by experiments at CERN-SPS (WA98) and BNL-RHIC (PHENIX) are