Non-tangential limits and the slope of trajectories of holomorphic semigroups of the unit disc

Abstract

Let $\Delta ⊊\mathbb{C}$ be a simply connected domain, let $f:\mathbb{D}\to \Delta$ be a Riemann map and let $\{z_k\}\subset \Delta$ be a compactly divergent sequence. Using Gromov's hyperbolicity theory, we show that $\{f^{-1}(z_k)\}$ converges non-tangentially to a point of $\partial \mathbb{D}$ if and only if there exists a simply connected domain $U⊊\mathbb{C}$ such that $\Delta \subset U$ and $\Delta$ contains a tubular hyperbolic neighborhood of a geodesic of $U$ and $\{z_k\}$ is eventually contained in a smaller tubular hyperbolic neighborhood of the same geodesic. As a consequence we show that if $({\varphi }_t)$ is a non-elliptic semigroup of holomorphic self-maps of $\mathbb{D}$ with Königs function $h$ and $h(\mathbb{D})$ contains a vertical Euclidean sector, then ${\varphi }_t(z)$ converges to the Denjoy-Wolff point non-tangentially for every $z\in \mathbb{D}$ as $t\to +\infty$. Using new localization results for the hyperbolic distance, we also construct an example of a parabolic semigroup which converges non-tangentially to the Denjoy-Wolff point but oscillating, in the sense that the slope of the trajectories is not a single point.

32 pages; 1 figure - final version, to appear in Trans. Amer. Math. Soc