Sub-riemannian geometry from intrinsic viewpoint
arXiv:1206.3093
Abstract
Gromov proposed to extract the (differential) geometric content of a sub-riemannian space exclusively from its Carnot-Carathéodory distance. One of the most striking features of a regular sub-riemannian space is that it has at any point a metric tangent space with the algebraic structure of a Carnot group, hence a homogeneous Lie group. Siebert characterizes homogeneous Lie groups as locally compact groups admitting a contracting and continuous one-parameter group of automorphisms. Siebert result has not a metric character. In these notes I show that sub-riemannian geometry may be described by about 12 axioms, without using any a priori given differential structure, but using dilation structures instead. Dilation structures bring forth the other intrinsic ingredient, namely the dilations, thus blending Gromov metric point of view with Siebert algebraic one.
These are the notes prepared for the course "Metric spaces with dilations and sub-riemannian geometry from intrinsic point of view", CIMPA research school on sub-riemannian geometry (2012). Unitary exposition based on several previous papers of mine, especially arXiv:0810.5042, hopefully with many details, explanations and some proofs which I previously skipped
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