For a regular sub-Riemannian manifold we study the Radon-Nikodym derivative of the spherical Hausdorff measure with respect to a smooth volume. We prove that this is the volume of the unit ball in the nilpotent approximation and it is always a continuous function. We then prove that up to dimension 4 it is smooth, while starting from dimension 5, in corank 1 case, it is C 3 (and C 4 on every smooth curve) but in general not C 5. These results answer to a question addressed by Montgomery about the relation between two intrinsic volumes that can be defined in a sub-Riemannian manifold, namely the Popp and the Hausdorff volume. If the nilpotent approximation depends on the point(that may happen starting from dimension 5), then they are not proportional, in general. © 2011 Springer-Verlag.

On the Hausdorff volume in sub-Riemannian geometry

Agrachev A.;Barilari D.;Boscain U.
2012

Abstract

For a regular sub-Riemannian manifold we study the Radon-Nikodym derivative of the spherical Hausdorff measure with respect to a smooth volume. We prove that this is the volume of the unit ball in the nilpotent approximation and it is always a continuous function. We then prove that up to dimension 4 it is smooth, while starting from dimension 5, in corank 1 case, it is C 3 (and C 4 on every smooth curve) but in general not C 5. These results answer to a question addressed by Montgomery about the relation between two intrinsic volumes that can be defined in a sub-Riemannian manifold, namely the Popp and the Hausdorff volume. If the nilpotent approximation depends on the point(that may happen starting from dimension 5), then they are not proportional, in general. © 2011 Springer-Verlag.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3401934
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