Multiplicity of non-contractible closed geodesics on Finsler compact space forms

Abstract

Let $M=S^n/\Gamma$ and $h$ be a nontrivial element of finite order $p$ in ${\pi }_1(M)$, where the integer $n,p\ge 2$, $\Gamma$ is a finite abelian group which acts freely and isometrically on the $n$-sphere and therefore $M$ is diffeomorphic to a compact space form. In this paper, we prove that for every irreversible Finsler compact space form $(M,F)$ with reversibility $\lambda$ and flag curvature $K$ satisfying \[ \frac{4p^2}{(p+1)^2} \big(\fracλ{λ+1} \big)^2 < K \leq 1,\;\;λ< \frac{p+1}{p-1}, \] there exist at least $n-1$ non-contractible closed geodesics of class $[h]$. In addition, if the metric $F$ is bumpy and \[ (\frac{4p}{2p+1})^2 (\fracλ{λ+1})^2 < K \leq 1,\;\;λ<\frac{2p+1}{2p-1}, \] then there exist at least $2[\frac{n+1}{2}]$ non-contractible closed geodesics of class $[h]$, which is the optimal lower bound due to Katok's example. For $C^4$-generic Finsler metrics, there are infinitely many non-contractible closed geodesics of class $[h]$ on $(M,F)$ if $\frac{{\lambda }^2}{(\lambda +1{)}^2}<K\le 1$ with $n$ being odd, or $\frac{{\lambda }^2}{(\lambda +1{)}^2}\frac{4}{(n-1{)}^2}<K\le 1$ with $n$ being even.

20 pages. arXiv admin note: text overlap with arXiv:1605.07292