Global existence for a class of reaction-diffusion systems with mass action kinetics and concentration-dependent diffusivities

In this work we study the existence of classical solutions for a class of reaction-diffusion systems with quadratic growth naturally arising in mass action chemistry when studying networks of reactions of the type $A_i+A_j \rightleftharpoons A_k$ with Fickian diffusion, where the diffusion coefficients might depend on time, space and on all the concentrations $c_i$ of the chemical species. In the case of one single reaction, we prove global existence for space dimensions $N\leq 5$. In the more restrictive case of diffusion coefficients of the type $d_i(c_i)$, we use an $L^2$-approach to prove global existence for $N\leq 9$. In the general case of networks of such reactions we extend the previous method to get global solutions for general diffusivities if $N\leq 3$ and for diffusion of type $d_i(c_i)$ if $N\leq 5$. In the latter quasi-linear case of $d_i(c_i)$ and for space dimensions $N=2$ and $N=3$, global existence holds for more than quadratic reactions. We can actually allow for more general rate functions including fractional power terms, important in applications. We obtain global existence under appropriate growth restrictions with an explicit dependence on the space dimension $N$.