The 4-string Braid group $B_4$ has property RD and exponential mesoscopic rank

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We prove that the braid group $B_4$ on 4 strings, as well as its central quotient $B_4/< z>$, have the property RD of Haagerup-Jolissaint. It follows that the automorphism group $\Aut(F_2)$ of the free group $F_2$ on 2 generators has property RD. We also prove that the braid group $B_4$ is a group of intermediate rank (of dimension 3). Namely, we show that both $B_4$ and its central quotient have exponential mesoscopic rank, i.e., that they contain exponentially many large flat balls which are not included in flats.
reference added, minor corrections

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Group Theory, Geometric Topology, Operator Algebras

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http://salesiana.dossiersoluciones.com/handle/123456789/218193

Consulte el texto completo en el siguiente enlace:

https://arxiv.org/abs/0809.0645
 http://arxiv.org/abs/0809.0645

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arXiv