Irrational l2-invariants arising from the lamplighter group
Group Theory
2015-04-28 v4 Geometric Topology
Abstract
We show that the Novikov-Shubin invariant of an element of the integral group ring of the lamplighter group Z_2 \wr Z can be irrational. This disproves a conjecture of Lott and Lueck. Furthermore we show that every positive real number is equal to the Novikov-Shubin invariant of some element of the real group ring of Z_2 \wr Z. Finally we show that the l2-Betti number of a matrix over the integral group ring of the group Z_p \wr Z, p>1, can be irrational, and so the groups Z_p \wr Z become the simplest known groups which give rise to irrational l2-Betti numbers.
Cite
@article{arxiv.1009.0229,
title = {Irrational l2-invariants arising from the lamplighter group},
author = {Łukasz Grabowski},
journal= {arXiv preprint arXiv:1009.0229},
year = {2015}
}
Comments
26 pages, 11 figures, v4: changes suggested by a referee (including fixing the proof of Lemma 11); To appear in Groups Geom. Dyn