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math.GR2023
Greenberg-Shalom's Commensurator Hypothesis and Applications
Nic Brody, David Fisher, Mahan Mj +1
We discuss many surprising implications of a positive answer to a question raised in some cases by Greenberg in the s and more generally by Shalom in the early s. We ref…
math.GR2022
Co-spectral radius of intersections
Mikolaj Fraczyk, Wouter van Limbeek
We study the behavior of the co-spectral radius of a subgroup of a discrete group under taking intersections. Our main result is that the co-spectral radius of an invariant…
math.GR2022
Commensurators of normal subgroups of lattices
David Fisher, Mahan Mj, Wouter Van Limbeek
We study a question of Greenberg-Shalom concerning arithmeticity of discrete subgroups of semisimple Lie groups with dense commensurators. We answer this question positively for no…