Sharp asymptotics of the first eigenvalue on some degenerating surfaces

Abstract

We study sharp asymptotics of the first eigenvalue on Riemannian surfaces obtained from a fixed Riemannian surface by attaching a collapsing flat handle or cross cap to it. Through a careful choice of parameters this construction can be used to strictly increase the first eigenvalue normalized by area if the initial surface has some symmetries. If these symmetries are not present we show that the first eigenvalue normalized by area strictly decreases for the same range of parameters. These results are the main motivation for the construction in [preprint, arXiv:1909.03105v2], where we show a monotonicity result for the normalized first eigenvalue without any symmetry assumptions.