Well-posedness and $L^1-L^p$ Smoothing Effect of the Porous Media Equation under Poincaré Inequality

We study the Cauchy problem for a weighted porous medium equation on $\mathbb{R}$ associated with a Gibbs probability measure $\pi =e^{-V}$. Under a Poincaré inequality for $\pi$ and the convexity assumption on $V$, we prove well-posedness and uniqueness of non-negative weak solutions with initial data in $L^1(\mathbb{R},\pi )$. We also establish an $L^1$–$L^p$ smoothing effect at every positive time. More precisely, for every admissible $p>1$, we show that the logarithm of the ratio between the $L^p(\mathbb{R},\pi )$ norm of the solution and its conserved $L^1(\mathbb{R},\pi )$ mass first decays at a super-exponential rate and then decays exponentially to zero. In particular, even if the initial datum belongs only to $L^1(\mathbb{R},\pi )$, the solution belongs to $L^p(\mathbb{R},\pi )$ for every finite $p>1$ and every $t>0$.