Photon production from non-equilibrium disoriented chiral condensates in   a longitudinal expansion : A theoretic framework
  A theoretical framework is developed for treating the quantization of the photons in a spacetime with a longitudinal expansion. This can be used to study the production of the photons through the non-equilibrium relaxation of a disoriented chiral condensate presumably formed in the expanding hot central region in ultra-relativistic heavy-ion collisions. These photons can be a signature of the formation of disoriented chiral condensates in the direct photon measurements of heavy-ion collisions. 
Da-Shin Lee, Yeo-Yie Charng, Kin-Wang Ng
hep-ph