Quasicircles and width of Jordan curves in $\mathbb{CP}^1$

Francesco Bonsante; Jeffrey Danciger; Sara Maloni; Jean-Marc Schlenker

doi:10.1112/blms.12438

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arXiv · 1908.09175

Quasicircles and width of Jordan curves in $\mathbb{CP}^1$

Francesco Bonsante·Jeffrey Danciger·Sara Maloni·Jean-Marc Schlenker

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Abstract

We study a notion of "width" for Jordan curves in $\mathbb{CP}^1$, paying special attention to the class of quasicircles. The width of a Jordan curve is defined in terms of the geometry of its convex hull in hyperbolic three-space. A similar invariant in the setting of anti de Sitter geometry was used by Bonsante-Schlenker to characterize quasicircles amongst a larger class of Jordan curves in the boundary of anti de Sitter space. By contrast to the AdS setting, we show that there are Jordan curves of bounded width which fail to be quasicircles. However, we show that Jordan curves with small width are quasicircles.

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Francesco Bonsante, Jeffrey Danciger, Sara Maloni, Jean-Marc Schlenker. 2019-08-24. Quasicircles and width of Jordan curves in $\mathbb{CP}^1$. https://doi.org/10.1112/blms.12438

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