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arXiv · 1009.0229

Irrational l2-invariants arising from the lamplighter group

Łukasz Grabowski
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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.

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Łukasz Grabowski. 2010-09-01. Irrational l2-invariants arising from the lamplighter group. https://arxiv.org/abs/1009.0229

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