About an H-theorem for systems with non-conservative interactions

We present some arguments in favor of an H-theorem for a generalization of the Boltzmann equation including non-conservative interactions and a linear Fokker-Planck-like thermostatting term. Such a non-linear equation describing the evolution of the single particle probability P-i(t) of being in state i at time t is a suitable model for granular gases and is referred to here as the Boltzmann-Fokker-Planck (BFP) equation. The conjectured H-functional, which appears to be non-increasing, is H-C(t)=Sigma P-i(i)(t) ln P-i(t)/Pi(i) with Pi(i) = lim(t ->infinity) P-i(t), in analogy with the H-functional of Markov processes. The extension to continuous states is straightforward. A simple proof can be given for the elastic BFP equation. A semi-analytical proof is also offered for the BFP equation for so-called inelastic Maxwell molecules. Other evidence is obtained by solving particular BFP cases through numerical integration or through 'particle schemes' such as the direct simulation Monte Carlo.