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Degenerate Umbilic Points of Analytic Surfaces

Differential Geometry 2025-02-04 v2

Abstract

Umbilics are points of a surface embedded in three space where normal curvatures are independent of direction. The (in)famous Carath\'{e}odory Conjecture states that a compact simply connected embedded surface has at least two umbilic points. A counterexample to this conjecture would be a surface whose principal foliation has index two at a single umbilic. All (purported) proofs of the Carath\'{e}odory Conjecture are based on analyses of the index of an umbilic, concluding that it is at most one. This investigation gives a much simpler geometric argument that the index of an umbilic on an analytic surface cannot be an integer larger than one, providing new insight into the Carath\'{e}odory Conjecture. The results also establish lower bounds for the index of an umbilic based on its degeneracy.

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Cite

@article{arxiv.2402.17060,
  title  = {Degenerate Umbilic Points of Analytic Surfaces},
  author = {John Guckenheimaer},
  journal= {arXiv preprint arXiv:2402.17060},
  year   = {2025}
}

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15 pages