Inhomogeneous Patlak-Keller-Segel models and Aggregation Equations with Nonlinear Diffusion in ${\text{Real}}^d$

Aggregation equations and Patlak-Keller-Segel (PKS) models for chemotaxis with nonlinear diffusion are popular models for nonlocal aggregation phenomenon and are a source of a number of interesting mathematical problems in nonlinear PDE. The purpose of this work is twofold. First, we continue our previous work, which focused on nonlocal aggregation, modeled with a convolution. The goal was to unify the local and global theory of these convolution-type models, including the identification of a sharp critical mass; however, some cases involving unbounded domains were left open. In particular, the biologically relevant case ${\text{Real}}^2$ was not treated. In this paper, we present an alternative proof of local existence, which now applies to ${\text{Real}}^d$ for all $d \geq 2$ and give global results that were left open. The proof departs from previous work in that it uses a more direct and intuitive regularization that constructs approximate solutions on ${\text{Real}}^d$ instead of on sequences of bounded domains. Second, this work develops the local, subcritical, and small data critical theory for a variety of Patlak-Keller-Segel models with spatially varying diffusion and decay rate of the chemo-attractant.