The horofunction boundary of a Gromov hyperbolic space

Abstract

We highlight a condition, the approaching geodesics property, on a proper geodesic Gromov hyperbolic metric space, which implies that the horofunction compactification is topologically equivalent to the Gromov compactification. It is known that this equivalence does not hold in general. We prove using rescaling techniques that the approaching geodesics property is satisfied by bounded strongly pseudoconvex domains of $$\mathbb {C}^q$$ endowed with the Kobayashi metric. We also show that bounded convex domains of $$\mathbb {C}^q$$ with boundary of finite type in the sense of D’Angelo satisfy a weaker property, which still implies the equivalence of the two said compactifications. As a consequence we prove that on those domains big and small horospheres as defined by Abate in (Math Z 198(2):225–238, 1988) coincide. Finally we generalize the classical Julia’s lemma, giving applications to the dynamics of non-expanding maps.