McKean-Vlasov limits of scaling-critical reaction-diffusion equations with random initial data

Abstract: We study a large class of scaling-critical reaction-diffusion equations in two spatial dimensions, where the initial data is white noise mollified at scale $\varepsilon^2$ and the reaction term is attenuated by a factor of $(\log\varepsilon^{-1})^{-1}$. We show that as $\varepsilon\to 0$, the solution converges to the solution of a McKean-Vlasov equation, which is Gaussian with standard deviation given by the solution to an ODE. Our result covers the case of the reaction term $f(u)=u^3$, and thus gives a new proof of the limiting behavior for the Allen-Cahn equation discovered in the recent work of Gabriel, Rosati, and Zygouras (Probab. Theory Related Fields 192: 1373-1446, 2025).