Pincement spectral en courbure de Ricci positive

Abstract

We show that for n dimensional manifolds whose the Ricci curvature is greater or equal to n-1 and for k in {1,...,n+1}, the k-th eigenvalue for the Laplacian is close to n if and only if the manifold contains a subset which is Gromov-Hausdorff close to the unit sphere of dimension k-1. For k=n+1, this gives a new proof of results of Colding and Petersen which show that the (n+1)-th eigenvalue is close to n if and only if the manifold is Gromov-Hausdorff close to the n-sphere.