Brownian particle in the curl of 2-d stochastic heat equations

Abstract

We study the long time behaviour of a Brownian particle evolving in a dynamic random environment. Recently, [G. Cannizzaro, L. Haunschmid-Sibitz, F. Toninelli, preprint arXiv:2106.06264] proved sharp $\sqrt{log}$-super diffusive bounds for a Brownian particle in the curl of (a regularisation of) the 2-d Gaussian Free Field (GFF) $\underline{\omega}$. We consider a one parameter family of Markovian and Gaussian dynamic environments which are reversible with respect to the law of $\underline{\omega}$. Adapting their method, we show that if $s\ge1$, with $s=1$ corresponding to the standard stochastic heat equation, then the particle stays $\sqrt{log}$-super diffusive, whereas if $s<1$, corresponding to a fractional heat equation, then the particle becomes diffusive. In fact, for $s<1$, we show that this is a particular case of [T. Komorowski, S. Olla, J. Func. Anal., 2003], which yields an invariance principle through a Sector Condition result. Our main results agree with the Alder-Wainwright scaling argument (see [B. Alder, T. Wainright, Phys. Rev. Lett. 1967]) used originally in [B. T\'oth, B. Valk\'o, J. Stat. Phys., 2012] to predict the $\log$-corrections to diffusivity. We also provide examples which display $log^a$-super diffusive behaviour for $a\in(0,1/2]$.