Internal characterization of non-horocyclically convex domains in the unit disk

Let D\mathbb{D} denote the unit disk, and let GG be a simply connected subdomain of D\mathbb{D}. Let C\mathcal{C} be the class of domains ΩD\Omega\subset\mathbb{D} of the form D1D2D_1\setminus\overline{D_2}, where each DjD_j is a hyperbolic disk in D\mathbb{D} and D1\partial D_1 and D2\partial D_2 intersect orthogonally at two points in D\mathbb{D}. For ΩC\Omega\in\mathcal{C}, let m(Ω)m(\Omega) denote the hyperbolic midpoint of the hyperbolically concave boundary arc D2D1\partial D_2\cap D_1 of Ω\Omega. Internal characterization conjecture. GG is not horocyclically convex in D\mathbb{D} if and only if there is a domain ΩC\Omega\in\mathcal{C} such that ΩG\Omega\subset G and m(Ω)GDm(\Omega)\in\partial G\cap\mathbb{D}. The paper presents this as a proposed characterization motivated by known results on lower bounds for the hyperbolic metric, but states that the related questions have no answers in the current work.

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Primary source

Juan Arango, Hugo Arbeláez and Diego Mejía, “On an Internal Characterization of Horocyclically Convex Domains in the Unit Disk”, arXiv:2407.21271 (2024).

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