Analysis of mass controlled reaction-diffusion systems with nonlinearities having critical growth rates

Abstract: We analyze semilinear reaction-diffusion systems that are mass controlled, and have nonlinearities that satisfy critical growth rates. The systems under consideration are only assumed to satisfy natural assumptions, namely the preservation of non-negativity and a control of the total mass. It is proved in dimension one that if nonlinearities have (slightly super-) cubic growth rates then the system has a unique global classical solutions. Moreover, in the case of mass dissipation, the solution is bounded uniformly in time in sup-norm. One key idea in the proof is the H\"older continuity of gradient of solutions to parabolic equation with possibly discontinuous diffusion coefficients and low regular forcing terms. When the system possesses additionally an entropy inequality, the global existence and boundedness of a unique classical solution is shown for nonlinearities satisfying a cubic intermediate sum condition, which is a significant generalization of cubic growth rates. The main idea in this case is to combine a modified Gagliardo-Nirenberg inequality and the newly developed $L^p$-energy method in \cite{morgan2021global,fitzgibbon2021reaction}. This idea also allows us to deal with the case of discontinuous diffusion coefficients in higher dimensions, which has \blue{only recently been touched} in the context of mass controlled reaction-diffusion systems.