The radiative transfer equations: diffusion approximation under accretiveness and compactness assumptions

When the mean free path of photons is small the radiative transfer equations may be approximated by a nonlinear angular diffusion equation. In order to find the diffusion equation, one uses accretiveness assumptions. But theses assumptions impose some conditions on the opacity. To overcome this inconvenient, we propose to study the solution of the radiative transfer equations by compactness techniques.