Published online by Cambridge University Press: 28 October 2014
We prove that on any compact manifold $M^{n}$ with boundary, there exists a conformal class
$C$ such that for any Riemannian metric
$g\in C$ of unit volume, the first positive eigenvalue of the Neumann Laplacian satisfies
${\it\lambda}_{1}(M^{n},g)<n\,\text{Vol}(S^{n},g_{\text{can}})^{2/n}$. We also prove a similar inequality for the first positive Steklov eigenvalue. The proof relies on a handle decomposition of the manifold. We also prove that the conformal volume of
$(M,C)$ is
$\text{Vol}(S^{n},g_{\text{can}})$, and that the Friedlander–Nadirashvili invariant and the Möbius volume of
$M$ are equal to those of the sphere. If
$M$ is a domain in a space form,
$C$ is the conformal class of the canonical metric.