An inhomogeneous porous medium equation with large data: well-posedness

We study solutions of a Euclidean weighted porous medium equation when the weight behaves at spacial infinity like $\mathrm{\mid }x{\mathrm{\mid }}^{-\gamma }$, for $\gamma \in [0,2)$, and is allowed to be singular at the origin. In particular we show local-in-time existence and uniqueness for a class of large initial data which includes as “endpoints” those growing at a rate of $\mathrm{\mid }x{\mathrm{\mid }}^{(2-\gamma )\mathrm{/}(m-1)}$, in a weighted $L^1$-average sense. We also identify global-existence and blow-up classes, whose respective forms strongly support the claim that such a growth rate is optimal, at least for positive solutions. As a crucial step in our existence proof we establish a local smoothing effect for large data without resorting to the classical Aronson-Bénilan inequality and using the Bénilan-Crandall inequality instead, which may be of independent interest since the latter holds in much more general settings.