Morse index bound of simple closed geodesics on 2-spheres and strong Morse inequalities

Abstract

Abstract We give a Morse-theoretic characterization of simple closed geodesics on Riemannian 2-spheres. On any Riemannian 2-sphere endowed with a generic metric, we show there exists a simple closed geodesic with Morse index 1, 2 and 3. In particular, for an orientable Riemannian surface, we prove strong Morse inequalities for the length functional applied to the space of simple closed curves.