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Bumpy metrics on spheres and minimal index growth

Differential Geometry · Submitted 5 Aug 2016

abstract compiled · 2026-09-23 · no language-model review

The authors' main claim The existence of two geometrically distinct closed geodesics on an $n$-dimensional sphere $S^n$ with a non-reversible and bumpy Finsler metric was shown independently by Duan--Long [7] and the author [27].

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arXiv ID1608.01937 (version 2)
Pith IDFB2TQD7M, Pith's permanent record of this paper and its review
CitationHans-Bert Rademacher. "Bumpy metrics on spheres and minimal index growth." arXiv:1608.01937 (2016). https://pith.science/paper/FB2TQD7M
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arXiv listing abstract v2. Results and the main claim are underlined; .

The existence of two geometrically distinct closed geodesics on an $n$-dimensional sphere $S^n$ with a non-reversible and bumpy Finsler metric was shown independently by Duan--Long [7] and the author [27]. We simplify the proof of this statement by the following observation: If for some $N \in \mathbb{N}$ all closed geodesics of index $\le N$ of a non-reversible and bumpy Finsler metric on $S^n$ are geometrically equivalent to the closed geodesic $c$ then there is a covering $c^r$ of minimal index growth, i.e. $${\rm ind}(c^{rm})=m {\rm ind}(c^r)-(m-1)(n-1)$$ for all $m \ge 1$ with ${\rm ind}\left(c^{rm}\right)\le N.$ But this leads to a contradiction for $N =\infty$ as pointed out by Goresky--Hingston [13]. We also discuss perturbations of Katok metrics on spheres of even dimension carrying only finitely many closed geodesics. For arbitrarily large $L>0$ we obtain on $S^2$ a metric of positive flag curvature carrying only two closed geodesics of length $<L$ which do not intersect.

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#sentencerolethe authors' own workstates the main conclusionstrength
s0 The existence of two geometrically distinct closed geodesics on an $n$-dimensional sphere $S^n$ with a non-reversible and bumpy Finsler metric was shown independently by Duan--Long [7] and the author [27]. background 1.00 0.43 0.19 asserted 1.00
s1 We simplify the proof of this statement by the following observation: If for some $N \in \mathbb{N}$ all closed geodesics of index $\le N$ of a non-reversible and bumpy Finsler metric on $S^n$ are geometrically equivalent to the closed geodesic $c$ then there is a covering $c^r$ of minimal index growth, i.e. $${\rm ind}(c^{rm})=m {\rm ind}(c^r)-(m-1)(n-1)$$ for all $m \ge 1$ with ${\rm ind}\left(c^{rm}\right)\le N.$ But this leads to a contradiction for $N =\infty$ as pointed out by Goresky--Hingston [13]. contribution 0.47 0.86 0.32 asserted 0.99
s2 We also discuss perturbations of Katok metrics on spheres of even dimension carrying only finitely many closed geodesics. contribution 0.97 0.71 0.05 asserted 0.77
s3 For arbitrarily large $L>0$ we obtain on $S^2$ a metric of positive flag curvature carrying only two closed geodesics of length $<L$ which do not intersect. result 0.99 0.89 0.23 asserted 1.00

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Original abstract

The existence of two geometrically distinct closed geodesics on an $n$-dimensional sphere $S^n$ with a non-reversible and bumpy Finsler metric was shown independently by Duan--Long [7] and the author [27]. We simplify the proof of this statement by the following observation: If for some $N \in \mathbb{N}$ all closed geodesics of index $\le N$ of a non-reversible and bumpy Finsler metric on $S^n$ are geometrically equivalent to the closed geodesic $c$ then there is a covering $c^r$ of minimal index growth, i.e. $${\rm ind}(c^{rm})=m {\rm ind}(c^r)-(m-1)(n-1)$$ for all $m \ge 1$ with ${\rm ind}\left(c^{rm}\right)\le N.$ But this leads to a contradiction for $N =\infty$ as pointed out by Goresky--Hingston [13]. We also discuss perturbations of Katok metrics on spheres of even dimension carrying only finitely many closed geodesics. For arbitrarily large $L>0$ we obtain on $S^2$ a metric of positive flag curvature carrying only two closed geodesics of length $<L$ which do not intersect.

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