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Mathematical Proceedings of the Cambridge Philosophical Society
Article . 1999 . Peer-reviewed
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Bestvina–Brady groups and the plus construction

Bestvina-Brady groups and the plus construction.
Authors: Howie, James;

Bestvina–Brady groups and the plus construction

Abstract

Summary: A recent result of \textit{M. Bestvina} and \textit{N. Brady} [Invent. Math. 129, No. 3, 445--470 (1997; Zbl 0888.20021), Theorem 8.7], shows that one of two outstanding questions has a negative answer; either there exists a group of cohomological dimension 2 and geometric dimension 3 (a counterexample to the Eilenberg-Ganea Conjecture [\textit{S. Eilenberg} and \textit{T. Ganea}, Ann. Math. (2) 65, 517--518 (1957; Zbl 0079.25401)]), or there exists a nonaspherical subcomplex of an aspherical 2-complex (a counterexample to the Whitehead Conjecture [\textit{J. H. C. Whitehead}, Ann. Math. (2) 42, 409--428 (1941; Zbl 0027.26404)]). More precisely, Bestvina and Brady construct a family of groups which are potential counterexamples to the Eilenberg-Ganea Conjecture, each of which has cohomological dimension 2. These are also examples of groups of type \(\text{FP}_2\) which are not finitely presented (see \textit{M. Bestvina} and \textit{N. Brady} [loc. cit.]). \textit{W. Dicks} and \textit{I. J. Leary} [Proc. Am. Math. Soc. 127, No. 2, 343--348 (1999; Zbl 0923.20032)] give an explicit way of obtaining presentations (on finite generating sets) for these groups. For some of these examples, it is shown in [\textit{M. Bestvina} and \textit{N. Brady}, loc. cit.] that any 2-dimensional classifying space would give rise to a counterexample to the Whitehead conjecture. We will refer to the examples cited above as Bestvina-Brady groups. These come equipped with natural, nonpositively curved cubical 3-dimensional classifying complexes, which we will call Bestvina-Brady complexes. In this short note, we show that these Bestvina-Brady complexes are (up to homotopy equivalence) formed by applying the Quillen plus construction to certain finite 2-complexes. From this, together with known facts about 2-complexes with aspherical plus constructions, we recover the result of Bestvina and Brady [loc. cit.] that the Bestvina-Brady groups act freely on acyclic 2-complexes, and hence have cohomological dimension at most 2. It also follows that these groups have free relation modules of finite rank and so are of type FF. Finally, we use our construction to give an alternative proof of the cited theorem of Bestvina and Brady; at least one of the Eilenberg-Ganea and Whitehead conjectures is false. We do not use the full force of the Morse-theoretical techniques developed in [\textit{M. Bestvina} and \textit{N. Brady}, loc. cit.], but will assume two results form that paper; the asphericity of the Bestvina-Brady complexes and the non-finite presentability of the Bestvina-Brady groups.

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Keywords

Generators, relations, and presentations of groups, Topological methods in group theory, presentations, Whitehead conjecture, Eilenberg-Ganea conjecture, finite generating sets, Braid groups; Artin groups, classifying space, groups of cohomological dimension 2, Two-dimensional complexes (manifolds), Bestvina-Brady groups, aspherical 2-complex, Quillen plus construction

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
5
Average
Average
Average
bronze