Coupled model for radiative transfer: Doppler effects, equilibrium, and nonequilibrium diffusion asymptotics

This paper is devoted to the asymptotic analysis of a coupled model arising in radiative transfer. The model consists of a kinetic equation satisfied by the specific intensity of radiation coupled to a diffusion equation satisfied by the material temperature. The interaction terms take into account both scattering and absorption/emission phenomena, as well as Doppler corrections. Two asymptotic regimes are identified, depending on the scaling assumptions about the physical parameters and observation scales. In the equilibrium regime, the system is driven only by the material temperature which satisfies a nonlinear drift-diffusion equation. In the nonequilibrium regime, the radiation temperature and the material temperature will be coupled by a system of nonlinear drift-diffusion equations.