Sobolev spaces in metric measure spaces: reflexivity and lower semicontinuity of slope

Abstract

In this paper we make a survey of some recent developments of the theory of Sobolev spaces $W^{1,q}(X,\sfd,\mm)$, $1<q<\infty$, in metric measure spaces $(X,\sfd,\mm)$. In the final part of the paper we provide a new proof of the reflexivity of the Sobolev space based on $\hat{I}“$-convergence; this result extends Cheeger's work because no Poincaré inequality is needed and the measure-theoretic doubling property is weakened to the metric doubling property of the support of $\mm$. We also discuss the lower semicontinuity of the slope of Lipschitz functions and some open problems.

The occasion for writing the paper has been the course given by the first author in Sapporo (July-August 2012). 46 pages. arXiv admin note: substantial text overlap with arXiv:1111.3730