Tubes in sub-Riemannian geometry and a Weyl's invariance result for curves in the Heisenberg groups

Abstract

The purpose of the paper is threefold: first, we prove optimal regularity results forthe distance from Ck submanifolds of general rank-varying sub-Riemannian structures. Then,we study the asymptotics of the volume of tubular neighbourhoods around such submanifolds.Finally, for the case of curves in the Heisenberg groups, we prove a Weyl’s invariance result:the volume of small tubes around curves does not depend on the way the curve is isometricallyembedded, but only on its Reeb angle. The proof does not need the computation of the actualvolume of the tube, and it is new even for the three-dimensional Heisenberg group