Finite and infinite speed of propagation for porous medium equations with nonlocal pressure

Abstract

We study a porous medium equation with fractional potential pressure: $${\partial }_{t}u=\nabla \cdot (u^{m-1}\nabla p),p=(-\Delta {)}^{-s}u,$$ for $m>1$, $0<s<1$ and $u(x,t)\ge 0$. The problem is posed for $x\in {\mathbb{R}}^N$, $N\ge 1$, and $t>0$. The initial data $u(x,0)$ is assumed to be a bounded function with compact support or fast decay at infinity. We establish existence of a class of weak solutions for which we determine whether the property of compact support is conserved in time depending on the parameter $m$, starting from the result of finite propagation known for $m=2$. We find that when $m\in [1,2)$ the problem has infinite speed of propagation, while for $m\in [2,3)$ it has finite speed of propagation. In other words $m=2$ is critical exponent regarding propagation.

37 pages, 3 figures