The zeros of the partition function of the pinning model

Rafael L. Greenblatt, Giambattista Giacomin

Published 2021-07-25Version 1

We aim at understanding for which (complex) values of the potential the pinning partition function vanishes. The pinning model is a Gibbs measure based on discrete renewal processes with power law inter-arrival distributions. We obtain some results for rather general inter-arrival laws, but we achieve a substantially more complete understanding for a specific one parameter family of inter-arrivals. We show, for such a specific family, that the zeros asymptotically lie (and densely fit) a closed curve that, without surprise, touches the real axis only in one point (the critical point of the model). We also perform a sharper analysis of the zeros close to the critical point and we exploit this analysis to approach the challenging problem of Griffiths singularities for the disordered pinning model. The techniques we exploit are both probabilistic and analytical. About the first ones, a central role is played by limit theorems for heavy tail random variables. And about the second ones, potential theory and singularity analysis of generating functions, along with their interplay, will be at the heart of several of our arguments.