Relative Entropy of a Freely Cooling Granular Gas
  The time evolution and stationary values of the entropy per particle of a homogeneous freely cooling granular gas, relative to the maximum entropy consistent with the instantaneous translational and rotational temperatures, is analyzed by means of a Sonine approximation involving fourth-degree cumulants. The results show a rich variety of dependencies of the relative entropy on time and on the coefficients of normal and tangential restitution, including a peculiar behavior in the quasi-smooth limit. 
Andr\'es Santos and Gilberto M. Kremer
cond-mat.soft cond-mat.stat-mech