Preprint

Inserted: 27 oct 2026
Last Updated: 27 oct 2026

Year: 2026

Abstract:

We prove that every critical spherical catenoid in a geodesic ball of hyperbolic three-space has Morse index four and nullity two. This resolves Medvedev’s index conjecture throughout the parameter range of the catenoid family. The kernel consists precisely of the normal components of rotations that preserve the center of the ball and tilt the axis of the catenoid. As a consequence, the radius of the supporting ball increases strictly along the family. The proof combines a global boundary inequality obtained from a Wronskian, a positive Dirichlet eigenfunction supplied by the time component of the unit normal, and a Riccati comparison for the angular mode k = 2. A ground-state identity then yields positivity of every angular mode k ≥ 2.

Keywords: Hyperbolic space, Morse index, Free boundary minimal surfaces, Robin eigenvalue problem, nullity, critical catenoid

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• 2610.35651v1.pdf