Geometric structures related to the braided Thompson groups
2021
In previous work, joint with Bux, Fluch, Marschler and Witzel, we proved that the braided Thompson groups are of type $${{\,\mathrm{F}\,}}_\infty $$
. The proof utilized certain contractible cube complexes, which in this paper we prove are $${{\,\mathrm{CAT}\,}}(0)$$
. We then use this fact to compute the geometric invariants $$\Sigma ^m(F_{{\text {br}}})$$
of the pure braided Thompson group $$F_{{\text {br}}}$$
. Only the first invariant $$\Sigma ^1(F_{{\text {br}}})$$
was previously known. A consequence of our computation is that as soon as a subgroup of $$F_{{\text {br}}}$$
containing the commutator subgroup $$[F_{{\text {br}}},F_{{\text {br}}}]$$
is finitely presented, it is automatically of type $${{\,\mathrm{F}\,}}_\infty $$
.
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