Analysis Seminar: Lior Alon (IAS) — Genericity results for metric graphs and the trace space

Date: 
Wed, 15/12/202114:00-15:00

Title
Genericity results for metric graphs and the trace space.

Abstract:
Many results in spectral geometry and analysis rely on Uhlenbeck's genericity result ('72) which states that given any manifold, for a Baire-generic choice of Riemannian metric, all eigenvalues of the associated Laplalacian are simple, with eigenfunctions that are Morse and does not vanish at their critical point. A similar result for metric graphs was given by Friedlander ('05) and Berkolaiko and Liu ('17). Given any fixed graph structure, for a Baire-generic choice of edge lengths, all eigenvalues of the Laplacian (with standard vertex conditions) are simple, with eigenfunctions that are Morse and do not vanish on vertices. However, apriori, the Baire-generic set of ``good'' edge lengths can have zero Lebesgue measure. 

In this talk, I will introduce a stronger notion of genericity, that implies full Lebesgue measure. To do so, I will define the ``Trace Space'', a moduli space of all eigenpairs associated with a graph structure. I will give an independent proof of the previous results, showing that they are in fact strongly generic. I will also show that any non-trivial homogenous relation on the traces must fail generically. This proof is algebraic in nature, uses ergodic theory, and is based on a conjecture of Colin de Verdiere which was recently proved by Kurasov and Sarnak.
I will not assume any prior knowledge in spectral geometry or metric graphs.