Hyperbolic triangular buildings without periodic planes of genus two

TL;DR

This paper investigates the existence of surface subgroups within certain hyperbolic triangular buildings, providing evidence that some groups may lack surface subgroups associated with periodic apartments, challenging assumptions in hyperbolic group theory.

Contribution

It introduces the first examples of groups acting simply transitively on hyperbolic triangular buildings that potentially lack surface subgroups from periodic apartments.

Findings

Most groups studied have no periodic apartments invariant under genus two surface actions.

The existence of such apartments would imply surface subgroups, but their absence suggests some groups may lack these subgroups.

These groups are the first candidates for hyperbolic groups without surface subgroups from periodic apartments.

Abstract

We study surface subgroups of groups acting simply transitively on vertex sets of certain hyperbolic triangular buildings. The study is motivated by Gromov's famous surface subgroup question: Does every one-ended hyperbolic group contain a subgroup which is isomorphic to the fundamental group of a closed surface of genus at least 2? Here we consider surface subgroups of the 23 torsion free groups acting simply transitively on the vertices of hyperbolic triangular buildings of the smallest non-trivial thickness. These groups gave the first examples of cocompact lattices acting simply transitively on vertices of hyperbolic triangular Kac-Moody buildings that are not right-angled. With the help of computer searches we show, that in most of the cases there are no periodic apartments invariant under the action of a genus two surface. The existence of such an action would imply the existence of a surface subgroup, but it is not known, whether the existence of a surface subgroup implies the existence of a periodic apartment. These groups are the first candidates for groups that have no surface subgroups arising from periodic apartments.