Dodziuk, J.,Linnell, P., Mathai, V., Schick, T. and Yates, S.: Approximating L2-invariants, and the Atiyah conjecture

Dodziuk, J., Linnell, P., Mathai, V., Schick, T. and Yates, S.: Approximating L2-invariants, and the Atiyah conjecture

Autor: Josef Dodziuk, Peter Linnell, Mathai Varghese, Thomas Schick, Stuart Yates
Titel: Approximating L2-invariants, and the Atiyah conjecture (dvi) (pdf)
Preprint SFB 478 "Geometrische Strukturen in der Mathematik" 170, Münster (2001)

Abstract: Let G be a torsion free discrete group and let \overline{Q} denote the field of algebraic numbers in C. We prove that \overline{Q}[G] fulfills the Atiyah conjecture if G lies in a certain class of groups D, which contains in particular all groups which are residually torsion free elementary amenable or which are residually free. This result implies that there are no non-trivial zero-divisors in C[G]. The statement relies on new approximation results for L2-Betti numbers over \overline{Q}[G], which are the core of the work done in this paper. Another set of results in the paper is concerned with certain number theoretic properties of eigenvalues for the combinatorial Laplacian on L2-cochains on any normal covering space of a finite CW complex. We establish the absence of eigenvalues that are transcendental numbers, whenever the covering transformation group is either amenable or in the Linnell class \mathcal{C}. We also establish the absence of eigenvalues that are Liouville transcendental numbers whenever the covering transformation group is either residually finite or more generally in a certain large bootstrap class \mathcal{G}. MSC: 55N25 (homology with local coefficients), 16S34 (group rings, Laurent rings), 46L50 (non-commutative measure theory)

Thomas Schick