On the cohomology of $GL_3$ of elliptic curves and Quillen's conjecture

Abstract

The paper provides a computation of the additive structure as well as a partial description of the Chern-class module structure of the cohomology of GL 3 over the function ring of an elliptic curve over a finite field. The computation is achieved by a detailed analysis of the isotropy spectral sequence for the action of GL 3 on the associated Bruhat-Tits building. This provides insights into the function field analogue of Quillen's conjecture on the structure of cohomology rings of arithmetic groups. The computations exhibit a lot of explicit classes which are torsion for the Chern-class ring. In some examples, even the torsion-free quotient of cohomology fails to be free. A possible variation of Quillen's conjecture is also discussed.