Conformal Green functions and Yamabe metrics of Sobolev regularity

We provide a full resolution of the Yamabe problem on closed 3-manifolds for Riemannian metrics of Sobolev class $W^{2,q}$ with $q>3$. This requires developing an elliptic theory for the conformal Laplacian for rough metrics and establishing existence, regularity and a delicate blow-up analysis for its Green function. Most of the analytical work is carried out in dimensions $n\ge 3$ and for $W^{2,q}$ Riemannian metrics with $q>\frac{n}{2}$ and should be of independent interest.