Geodesic
Metric characteristics of classes of compact sets on Carnot groups with sub-Lorentzian structure
Vladikavkazskij matematičeskij žurnal, Tome 26 (2024) no. 3, pp. 56-64 
M. B. Karmanova. Metric characteristics of classes of compact sets on Carnot groups with sub-Lorentzian structure. Vladikavkazskij matematičeskij žurnal, Tome 26 (2024) no. 3, pp. 56-64. http://geodesic.mathdoc.fr/item/VMJ_2024_26_3_a4/
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     title = {Metric characteristics of classes of compact sets on {Carnot} groups with {sub-Lorentzian} structure},
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Voir la notice de l'article provenant de la source Math-Net.Ru

We consider classes of mappings of Carnot groups that are intrinsically Lipschitz and defined on compact subsets, and describe the metric characteristics of their images under the condition that a sub-Lorentzian structure is introduced on the image. This structure is a sub-Riemannian generalization of Minkowski geometry. One of its features is the unlimitedness of the balls constructed with respect to the intrinsic distance. In sub-Lorentzian geometry, the study of spacelike surfaces whose intersections with such balls are limited, is of independent interest. If the mapping is defined on an open set, then the formulation of space-likeness criterion reduces to considering the connectivity component of the intersection containing the center of the ball and analyzing the properties of the sub-Riemannian differential matrix. If the domain of definition of the mapping is not an open set, then the question arises what conditions can be set on the mapping that guarantee the boundedness of the intersection of the image of a compact set with a sub-Lorentzian ball. In this article, this problem is resolved: we consider that part of the intersection that can be parameterized by the connectivity component of the intersection of the image of the sub-Riemannian differential and the ball. In addition, using such local parameterizations, a set function is introduced, which is constructed similarly to Hausdorff measure. We show that this set function is also a measure. As an application, the sub-Lorentzian area formula is established.

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