Mixing for generic rough shear flows

Abstract

We study mixing and diffusion properties of passive scalars driven by $generic$ rough shear flows. Genericity is here understood in the sense of prevalence and (ir)regularity is measured in the Besov-Nikolskii scale $B^α_{1, \infty}$, $α\in (0, 1)$. We provide upper and lower bounds, showing that in general inviscid mixing in $H^{1/2}$ holds sharply with rate $r(t) \sim t^{1/(2 α)}$, while enhanced dissipation holds with rate $r(ν) \sim ν^{α/ (α+2)}$. Our results in the inviscid mixing case rely on the concept of $ρ$-irregularity, first introduced by Catellier and Gubinelli (Stoc. Proc. Appl. 126, 2016) and provide some new insights compared to the behavior predicted by Colombo, Coti Zelati and Widmayer (arXiv:2009.12268, 2020).