Inhomogeneous relativistic Boltzmann equation near vacuum in the   Robertson-Walker space-time
  In this paper, we consider the Cauchy problem for the relativistic Boltzmann equation with near vacuum initial data where the distribution function depends on the time, the position and the impulsion. The collision kernel considered here is for the hard potentials case and the background space-time in which the study is done is the Robertson-Walker space-time. Unique global (in time) mild solution is obtained in a suitable weighted space. 
Etienne Takou, Fidele L. Ciake Ciake
gr-qc