Find Paper, Faster
Example：10.1021/acsami.1c06204 or Chem. Rev., 2007, 107, 2411-2502
Commutators, commensurators, and PSL2(Z)
Journal of Topology  (IF1.582),  Pub Date : 2021-07-09, DOI: 10.1112/topo.12200
Thomas Koberda, Mahan Mj

Let $H < PSL 2 ( Z )$ be a finite index normal subgroup which is contained in a principal congruence subgroup, and let $Φ ( H ) ≠ H$ denote a term of the lower central series or the derived series of $H$. In this paper, we prove that the commensurator of $Φ ( H )$ in $PSL 2 ( R )$ is discrete. We thus obtain a natural family of thin subgroups of $PSL 2 ( R )$ whose commensurators are discrete, establishing some cases of a conjecture of Shalom.