Recurrent and irregular orbits of the horocyclic flow on the unit tangent bundle of the untwisted flute
Amadou Sy
TL;DR
The paper investigates the horocycle flow on the unit tangent bundle of untwisted flute surfaces, focusing on when the horocycle orbit closure intersects the geodesic orbit of a vector $u$. By leveraging horocyclic convergence criteria, limit-set stratification, and the geometry of geometrically infinite Fuchsian groups, the authors prove that for a quasi-minimizing half-geodesic $u(\mathbb{R}^{+})$ avoiding all closed geodesics and with $h_{\mathbb{R}}u$ neither closed nor dense, the set $T_{u}=\{t\in\mathbb{R}: g_t u\in \overline{h_{\mathbb{R}}u}\}$ is trivial, i.e., $T_{u}=\{0\}$. They construct an explicit untwisted flute from a nested-Schottky group to realize an infinite quasi-minimizing ray with infinite asymptotic fineness and non-dense horocycle dynamics, yet still satisfy $T_{u}=\{0\}$. The work also proves structural properties of $T_{u}$ as a nonempty closed semigroup and provides a concrete infinite-example showing $T_{u}$ can be infinite in other setups. These results illuminate how horocycle non-minimality behaves in infinite-type hyperbolic surfaces and respond to questions about closures of horocycle orbits on flutes. The findings have implications for understanding the interaction between horocycle and geodesic dynamics on geometrically infinite surfaces and for Bellis’ questions on flute surfaces.
Abstract
The aim of this article is to show that if there exists $u \in Ω_{h} \subset T^{1}S$ an infinite quasi-minimizing ray which do not intersect any closed geodesic on the surface $S$ (untwisted flute), then $T_{u}=\{ t \in \mathbb{R} \; ; \; g_{t}u \in \overline{h_{\mathbb{R}}u} \}=\{0\}$.
