Blow-up and global existence for the inhomogeneous porous medium equation with reaction

Abstract

We study finite time blow-up and global existence of solutions to the Cauchy problem for the porous medium equation with a variable density $\rho(x)$ and a power-like reaction term. We show that for small enough initial data, if $\rho(x)\sim \frac{1}{\left(\log|x|\right)^{\alpha}|x|^{2}}$ as $|x|\to \infty$, then solutions globally exist for any $p>1$. On the other hand, when $\rho(x)\sim\frac{\left(\log|x|\right)^{\alpha}}{|x|^{2}}$ as $|x|\to \infty$, if the initial datum is small enough then one has global existence of the solution for any $p>m$, while if the initial datum is large enough then the blow-up of the solutions occurs for any $p>m$. Such results generalize those established in [27] and [28], where it is supposed that $\rho(x)\sim |x|^{-q}$ for $q>0$ as $|x|\to \infty$.