The lower algebraic $K$-theory of virtually cyclic subgroups of the braid groups of the sphere and of $\mathbb{Z}[B_4(\mathbb{S}^2)]$ - Archive ouverte HAL
Pré-Publication, Document De Travail Année : 2012

The lower algebraic $K$-theory of virtually cyclic subgroups of the braid groups of the sphere and of $\mathbb{Z}[B_4(\mathbb{S}^2)]$

Résumé

We study $K$-theoretical aspects of the braid groups $B_n(\mathbb{S}^{2})$ on $n$ strings of the $2$-sphere, which by results of the second two authors, are known to satisfy the Farrell-Jones fibred isomorphism conjecture~\cite{JM}. In light of this, in order to determine the algebraic $K$-theory of the group ring $\mathbb{Z}[B_n(\mathbb{S}^{2})]$, one should first compute that of its virtually cyclic subgroups, which were classified by D.~L.~Gonçalves and the first author. We calculate the Whitehead and $K_{-1}$-groups of the group rings of the finite subgroups (dicyclic and binary polyhedral) of $B_n(\mathbb{S}^{2})$ for all $4\leq n\leq 11$. Some new phenomena occur, such as the appearance of torsion for the $K_{-1}$-groups. We then go on to study the case $n=4$ in detail, which is the smallest value of $n$ for which $B_n(\mathbb{S}^{2})$ is infinite. We show that $B_n(\mathbb{S}^{2})$ is an amalgamated product of two finite groups, from which we are able to determine a universal space for proper actions of the group $B_n(\mathbb{S}^{2})$. We also calculate the algebraic $K$-theory of the infinite virtually cyclic subgroups of $B_n(\mathbb{S}^{2})$, including the Nil groups of the quaternion group of order $8$. This enables us to determine the lower algebraic $K$-theory of $\mathbb{Z}[B_n(\mathbb{S}^{2})]$.
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Dates et versions

hal-00734244 , version 1 (21-09-2012)
hal-00734244 , version 2 (29-06-2018)

Identifiants

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John Guaschi, Daniel Juan-Pineda, Silvia Millán-López. The lower algebraic $K$-theory of virtually cyclic subgroups of the braid groups of the sphere and of $\mathbb{Z}[B_4(\mathbb{S}^2)]$. 2012. ⟨hal-00734244v1⟩
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