Geometry of Carnot--Carathéodory Spaces, Differentiability and Coarea Formula

Karmanova, Maria; Vodopyanov, Sergey

Geometry of Carnot--Carathéodory Spaces, Differentiability and Coarea Formula

Authors

Description

We give a simple proof of Gromov's Theorem on nilpotentization of vector fields, and exhibit a new method for obtaining quantitative estimates of comparing geometries of two different local Carnot groups in Carnot--Carathéodory spaces with $C^{1,α}$-smooth basis vector fields, $α\in[0,1]$. From here we obtain the similar estimates for comparing geometries of a Carnot--Carathéodory space and a local Carnot group. These two theorems imply basic results of the theory: Gromov type Local Approximation Theorems, and for $α>0$ Rashevski\vı-Chow Theorem and Ball--Box Theorem, etc. We apply the obtained results for proving $hc$-differentiability of mappings of Carnot--Carathéodory spaces with continuous horizontal derivatives. The latter is used in proving the coarea formula for some classes of contact mappings of Carnot--Carathéodory spaces.
94 pages