We study a nonlinear hyperbolic system of balance laws that arises from an entropy-based moment closure of transfer radiative equations, and that involves a small parameter $\epsilon$. Under physical assumptions, global existence for Cauchy problems with smooth and small data is established through the energy method.
"Global existence of smooth solutions for radiative transfer equations." Adv. Differential Equations 12 (2) 201 - 219, 2007.