Parabolic regularisation for increasing functions and applications to reaction-diffusion and reaction-cross-diffusion systems

Abstract: We propose a careful study of the parabolic equation $a\partial_t w - \Delta w = f$ with a rough coefficient $a$, homogeneous Neumann boundary conditions, and the special assumption $\partial_t w \ge 0$. The H\"older regularity estimate obtained from this study is used to obtain quick proofs of already known results of regularity for quadratic reaction-diffusion systems coming out of reversible chemistry, and to get new results for reaction-cross diffusion systems including the triangular Shigesada-Kawasaki-Teramoto system with moderately growing reaction terms.