The Weinstock inequality for convex domains in hyperbolic space

Abstract

We prove the Weinstock inequality for the first Steklov eigenvalue of convex domains in hyperbolic space ${\mathbb{H}}^n$, resolving Open Question 4.27 of Colbois-Girouard-Gordon-Sher(2024) for the remaining case $n=3$. Our argument replaces the global monotonicity required in earlier work Gu-Li-Wan(2025) with a one-crossing property, which is established via an explicit slope comparison. The proof works uniformly for all $n\ge 3$.