Discreteness-induced spatial chaos versus fluctuation-induced spatial order in stochastic Turing pattern formation

We investigate Turing pattern formation in a stochastic reaction-diffusion model defined on $N$ lattice sites, where each lattice site is associated with a reaction vessel of volume $\Omega$. We focus on a regime where spatial discreteness plays a crucial role, namely when the characteristic length of patterns is comparable to the lattice spacing. In this setting, we compare two different limiting procedures and show that they lead to qualitatively different outcomes. If we first take the deterministic limit $\Omega \to \infty$ and then the long-time limit $t \to \infty$, the stationary solutions of the corresponding spatially discrete deterministic equations become spatially chaotic in the limit $N\to\infty$. In contrast, if we first take the limit $t \to \infty$ and then take an appropriate limit of $\Omega \to \infty$ and $N\to\infty$, the resulting patterns are spatially periodic.