English

Hyperbolic geometry of shapes of convex bodies

Differential Geometry 2021-09-02 v2

Abstract

We use the intrinsic area to define a distance on the space of homothety classes of convex bodies in the nn-dimensional Euclidean space, which makes it isometric to a convex subset of the infinite dimensional hyperbolic space. The ambient Lorentzian structure is an extension of the intrinsic area form of convex bodies, and Alexandrov--Fenchel Inequality is interpreted as the Lorentzian reversed Cauchy--Schwarz Inequality. We deduce that the space of similarity classes of convex bodies has a proper geodesic distance with curvature bounded from below by 1-1 (in the sense of Alexandrov). In dimension 33, this space is homeomorphic to the space of distances with non-negative curvature on the 22-sphere, and this latter space contains the space of flat metrics on the 22-sphere considered by W.P.~Thurston. Both Thurston's and the area distances rely on the area form. So the latter may be considered as a generalization of the "real part" of Thurston's construction.

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Cite

@article{arxiv.1806.09524,
  title  = {Hyperbolic geometry of shapes of convex bodies},
  author = {Clément Debin and François Fillastre},
  journal= {arXiv preprint arXiv:1806.09524},
  year   = {2021}
}

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