On trace set of hyperbolic surfaces and a conjecture of Sarnak and Schmutz
Yanlong Hao
TL;DR
This work studies the trace set $Tr(\Gamma)$ of Fuchsian lattices and its arithmetic implications. It proves a strong version of Schmutz’s conjecture for non-uniform lattices: linear growth of $Tr(\Gamma)$ characterizes arithmeticity, and demonstrates that for a fixed genus $g\ge 3$ the cocompact embeddings with trace-growth exceeding $n^{2-\varepsilon}$ occupy positive Weil-Petersson volume, with an explicit asymptotic description. The authors adapt Schmutz’s geometric ideas into a powerful algebraic framework, establishing rationality properties of derived subgroups and employing density arguments via $\mathbb{Z}$-affine constructions and Dirichlet-type estimates to constrain trace sets. They extend trace-set growth analysis to the cocompact regime on high-genus surfaces, using multicurves, Cheeger constants, and Mirzakhani’s growth results to show WP-volume prevalence of large-growth instances. Overall, the paper links trace-set growth to arithmeticity and provides volume-analytic insights into trace-growth phenomena on moduli spaces of hyperbolic surfaces.
Abstract
In this paper, we investigate the trace set of a Fuchsian lattice. There are two results of this paper: the first is that for a non-uniform lattice, we prove Scmutz's conjecture: the trace set of a Fuchsian lattice exhibits linear growth if and only if the lattice is arithmetic. Additionally, we show that for a fixed surface group of genus bigger than 2 and any positive number $ε$, te set of cocompact lattice embedding such that their growth rate of trace set exceeds $n^{2-ε}$ has positive Weil-Petersson volume. We also provide an asymptotic analysis of the volume of this set.
