4 papers
Congruence rigidity of algebraic groups
Adrian Baumann, Holger Kammeyer
We identify the simple algebraic groups over number fields that are, in a suitable sense, determined by their finite adele points. Assuming CSP and Grothendieck rigidity, our resul…
On the Euler characteristic of -arithmetic groups
Holger Kammeyer, Giada Serafini
We show that the sign of the Euler characteristic of an -arithmetic subgroup of a simple algebraic group depends on the -congruence completion only, except possibly in type $…
Infinite groups from the profinite point of view
Holger Kammeyer, Steffen Kionke
We survey recent work ranging around the question in how far a group, or a property of a group, is determined by the set of finite quotient groups. Our focus lies on -arithmetic…
Profiniteness of higher rank volume
Holger Kammeyer, Steffen Kionke, Ralf Köhl
We show that the covolume of an irreducible lattice in a higher rank semisimple Lie group with the congruence subgroup property is determined by the profinite completion. Without r…