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PreprintCC BY 4.0arXiv

Index and nullity of critical spherical catenoids in hyperbolic three-space

  • Ivan Dorofeev
  • Alexander Pigazzini
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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 consequences, the radius of the supporting ball increases strictly along the family, and each critical spherical catenoid admits a smooth family of free boundary constant mean curvature deformations in its supporting ball. 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.

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Cite

BibTeXRIS
BibTeX
@misc{dorofeev2026index,
  title = {{Index and nullity of critical spherical catenoids in hyperbolic three-space}},
  author = {Ivan Dorofeev and Alexander Pigazzini},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.35651},
  eprint = {2610.35651},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.35651},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - Index and nullity of critical spherical catenoids in hyperbolic three-space
AU  - Ivan Dorofeev
AU  - Alexander Pigazzini
PY  - 2026
DA  - 2026/10/29
PB  - arXiv
DO  - 10.48550/arxiv.2610.35651
UR  - https://arxiv.org/abs/2610.35651
AB  - 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 consequences, the radius of the supporting ball increases strictly along the family, and each critical spherical catenoid admits a smooth family of free boundary constant mean curvature deformations in its supporting ball. 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.
ER  -