Microlocal analysis of singular measures

The purpose of this article is to investigate the structure of singular measures from a microlocal perspective. Motivated by the result of De Philippis-Rindler (Ann Math 184:1017-1039, 2016), and the notions of wave cones of Murat-Tartar (Ann Scuola Norm Sup Pisa Cl Sci 5:489-507, 1978; Proceedings of the International Meeting on Recent Methods in Nonlinear Analysis (Rome, 1978), pp 245-256. Pitagora, 1979; Nonlinear Analysis and Mechanics: Heriot-Watt Symposium, vol IV. Research Notes in Mathematics, vol 39, pp 136-212. Pitman, 1979; Systems of Nonlinear Partial Differential Equations (Oxford, 1982). NATO Advanced Science Institutes Series C: Mathematical and Physical Sciences, vol 111, pp 263-285. Reidel, 1983) and of polarisation set of Denker (J Funct Anal 46:351-372, 1982) we introduce a notion of L-1-regularity wave front set for scalar and vector distributions. Our main result is a proper microlocal characterisation of the support of the singular part of tempered Radon measures and of their polar functions at these points. The proof is based on De Philippis-Rindler's approach reinforced by microlocal analysis techniques and some extra geometric measure theory arguments. We deduce a sharp L-1 elliptic regularity result which appears to be new even for scalar measures and which enlightens the interest of the techniques from geometric measure theory to the study of harmonic analysis questions. For instance we prove that Psi L-0(1) boolean AND M-loc subset of L-loc(1), and in particular we obtain L-1 elliptic regularity results as Delta u is an element of L-loc(1), D-u(2) is an element of M-loc double right arrow D(2)u is an element of L-loc(1). We also deduce several consequences including extensions of the results in De Philippis and Rindler (2016) giving constraints on the polar function at singular points for measures constrained by a PDE, and of Alberti's rank one theorem. Finally, we also illustrate the interest of this microlocal approach with a result of propagation of singularities for constrained measures.