Cosmology with bulk pressure
  Different cooling rates of interacting fluid components of the expanding cosmic medium give rise to entropy producing bulk stresses. With the help of effective bulk pressures, on the other hand, one may phenomenologically take into account cosmological particle production processes. We report on recent progress in bulk viscous cosmology both on the phenomenological level and on the level of relativistic kinetic theory. 
Winfried Zimdahl, Diego Pavon and Josep Triginer