Equation of state for directed percolation
  Using field-theoretic renormalization group methods we calculate the equation of state for non-equilibrium systems belonging to the universality class of directed percolation (Gribov process) to second order in epsilon = 4-d. By introducing a parametric representation the result can be written to this order in a very simple form. We use our result to obtain a universal amplitude ratio to second order in epsilon. 
H. K. Janssen, Ue. Kutbay, K. Oerding (U. Duesseldorf)