Properties of the Boltzmann equation in the classical approximation

Abstract : We study the Boltzmann equation with elastic point-like scalar interac-tions in two different versions of the the classical approximation. Although solving numerically the Boltzmann equation with the unapproximated col-lision term poses no problem, this allows one to study the effect of the ultraviolet cutoff in these approximations. This cutoff dependence in the classical approximations of the Boltzmann equation is closely related to the non-renormalizability of the classical statistical approximation of the underlying quantum field theory. The kinetic theory setup that we con-sider here allows one to study in a much simpler way the dependence on the ultraviolet cutoff, since one has also access to the non-approximated result for comparison.