Green-Kubo Expressions for a Granular Gas
  The transport coefficients for a gas of smooth, inelastic hard spheres are obtained from the Boltzmann equation in the form of Green-Kubo relations. The associated time correlation functions are not simply those constructed from the fluxes of conserved densities. Instead, fluxes constructed from the reference local homogeneous distribution occur as well. The analysis exposes potential problems associated with a straightforward extension of linear response methods to granular systems. 
James W. Dufty, J. Javier Brey