Thermal photons from fluctuating initial conditions
  Event-by-event fluctuations of initial QCD-matter density produced in heavy-ion collisions at RHIC enhance the production of thermal photons significantly in the region $2 \le p_T \le 4$ GeV/$c$ compared to a smooth initial-state averaged profile in the ideal hydrodynamic calculation. This enhancement is a an early time effect due to the presence of hotspots or over-dense regions in the fluctuating initial state. The effect of fluctuations is found to be stronger in peripheral than in central collisions. 
Rupa Chatterjee, Hannu Holopainen, Thorsten Renk, and Kari J. Eskola
hep-ph