Regularity of solutions of the fractional porous medium flow with exponent 1/2

Abstract

We study the regularity of a porous medium equation with nonlocal diffusion effects given by an inverse fractional Laplacian operator. The precise model is $u_t=\nabla \cdot (u\nabla (-\Delta {)}^{-1/2}u).$ For definiteness, the problem is posed in $\{x\in {\mathbb{R}}^N,t\in \mathbb{R}\}$ with nonnegative initial data $u(x,0)$ that are integrable and decay at infinity. Previous papers have established the existence of mass-preserving, nonnegative weak solutions satisfying energy estimates and finite propagation, as well as the boundedness of nonnegative solutions with $L^1$ data, for the more general family of equations $u_t=\nabla \cdot (u\nabla (-\Delta {)}^{-s}u)$, $0<s<1$. Here we establish the $C^{\alpha }$ regularity of such weak solutions in the difficult fractional exponent case $s=1/2$. For the other fractional exponents $s\in (0,1)$ this Hölder regularity has been proved in $[5]$. The method combines delicate De Giorgi type estimates with iterated geometric corrections that are needed to avoid the divergence of some essential energy integrals due to fractional long-range effects.

arXiv comment35 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1201.6048