Wildest $\mathrm{SL}_2$-tilings
Andrei Zabolotskii
TL;DR
This study investigates the maximal wildness of SL_2-tilings by formalizing wild density as the limiting proportion of wild entries in large neighborhoods. It proves a sharp dichotomy: over the integers, the wild density is at most $2/5$ with a construction achieving this bound, while over rings with zero divisors, a periodic construction yields density $1$, including a concrete N=36 example where every entry is wild. The results reveal how local determinant constraints interact with global tiling patterns (e.g., Cairo pentagonal tessellations) and show that maximal wildness depends on the underlying ring. This advances the understanding of wild SL_2-tilings beyond tame friezes and connects to combinatorial tilings and modular arithmetic.
Abstract
Tame SL$_2$-tilings are related to Farey graph and friezes; much less is known about wild (not tame) SL$_2$-tilings. In this note, we demonstrate SL$_2$-tilings that are maximally wild: we prove that the maximum wild density of an integer SL$_2$-tiling is $\tfrac25$ and present SL$_2$-tilings over $\mathbb{Z}/N\mathbb{Z}$ with wild density 1.
