A nonequilibrium renormalization group approach to turbulent reheating
  We use nonequilibrium renormalization group (RG) techniques to analyze the thermalization process in quantum field theory, and by extension reheating after inflation. Even if at a high scale $\Lambda$ the theory is described by a non-dissipative $\lambda\phi^{4}$ theory, the RG running induces nontrivial noise and dissipation. For long wavelength, slowly varying field configurations, the noise and dissipation are white and ohmic, respectively. The theory will then tend to thermalize to an effective temperature given by the fluctuation-dissipation theorem. 
Juan Zanella and Esteban Calzetta