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arXiv 0811.3422math.GRmath.FA
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不可单位表示和随机森林

Non-unitarisable representations and random forests

Inessa Epstein, Nicolas Monod

摘要:

我们建立了一个连接Dixlane的unitability问题和预期程度的随机森林组。因此,如果一个剩余有限群的第一个L2-贝蒂数不为零,或者如果它是以非平凡代价生成的,则它是不可单位的。我们的准则也适用于由D. Osin,从而提供了第一个例子,非unitable集团不包含一个非阿贝尔自由子群。

英文摘要:

We establish a connection between Dixmier's unitarisability problem and the expected degree of random forests on a group. As a consequence, a residually finite group is non-unitarisable if its first L2-Betti number is non-zero or if it is finitely generated with non-trivial cost. Our criterion also applies to torsion groups constructed by D. Osin, thus providing the first examples of non-unitarisable groups not containing a non-Abelian free subgroup.

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