Spectrum and combinatorics of two-dimensional Ramanujan complexes
arXiv:1406.6666 · doi:10.1007/s11856-019-1828-z
Abstract
Ramanujan graphs have extremal spectral properties, which imply a remarkable combinatorial behavior. In this paper we compute the high dimensional Hodge-Laplace spectrum of Ramanujan triangle complexes, and show that it implies a combinatorial expansion property, and a pseudo-randomness result. For this purpose we prove a Cheeger-type inequality and a mixing lemma of independent interest.