Topological obstructions to continuity of Orlicz-Sobolev mappings of finite distortion (1804.07625v1)
Abstract: In the paper we investigate continuity of Orlicz-Sobolev mappings $W{1,P}(M,N)$ of finite distortion between smooth Riemannian $n$-manifolds, $n\geq 2$, under the assumption that the Young function $P$ satisfies the so called divergence condition $\int_1\infty P(t)/t{n+1}\, dt=\infty$. We prove that if the manifolds are oriented, $N$ is compact, and the universal cover of $N$ is not a rational homology sphere, then such mappings are continuous. That includes mappings with $Df\in Ln$ and, more generally, mappings with $Df\in Ln\log{-1}L$. On the other hand, if the space $W{1,P}$ is larger than $W{1,n}$ (for example if $Df\in Ln\log{-1}L$), and the universal cover of $N$ is homeomorphic to $\mathbb{S}n$, $n\neq 4$, or is diffeomorphic to $\mathbb{S}n$, $n=4$, then we construct an example of a mapping in $W{1,P}(M,N)$ that has finite distortion and is discontinuous. This demonstrates a new global-to-local phenomenon: both finite distortion and continuity are local properties, but a seemingly local fact that finite distortion implies continuity is a consequence of a global topological property of the target manifold $N$.