Results on the homotopy type of the spaces of locally convex curves on $S^3$

Abstract

A curve $γ: [0,1] \rightarrow S^n$ of class $C^k$ ($k \geqslant n$) is locally convex if the vectors $γ(t), γ'(t), γ"(t), \cdots, γ^{(n)}(t)$ are a positive orthonormal basis to $R^{n+1}$ for all $t \in [0,1]$. Given an integer $n \geq 2$ and $Q \in SO_{n+1}$, let $LS^n(Q)$ be the set of all locally convex curves $γ: [0,1] \rightarrow S^n$ with fixed initial and final Frenet frame $F_γ(0)=I$ and $F_γ(1)=Q$. Saldanha and Shapiro proved that there are just finitely many non-homeomorphic spaces among $LS^n(Q)$ when $Q$ varies in $SO_{n+1}$ (in particular, at most $3$ for $n=3$). For any $n \geqslant 2$, the homotopy type of one of these spaces is well-known, but not of the others. For $n=2$, Saldanha determined the homotopy type of the spaces $LS^2(Q)$. The purpose of this work is to study the case $n=3$. We will obtain information on the homotopy type of one of these $2$ other spaces, allowing us to conclude that its connected components are not homeomorphic to the connected components of the known space.