arXiv subjects

Simon St John-Green

Publications and source records attributed to Simon St John-Green.

5 recordsLinked to original sources

arXiv2017

Quasi-automorphisms of the infinite rooted 2-edge-coloured binary tree

We study the group $QV$, the self-maps of the infinite $2$-edge coloured binary tree which preserve the edge and colour relations at cofinitely many locations. We introduce related groups $QF$, $QT$, $\tilde{Q}T$, and $\tilde{Q}V$, prove that $QF$, $\tilde{Q}T$, and $\tilde{Q}V$ are of type $\mathrm{F}_\infty$, and calculate finite presentations for them. We calculate the normal subgroup structure and rational homology of all $5$ groups, the Bieri--Neumann--Strebel--Renz invariants of $QF$, and discuss the relationship of all $5$ groups with other generalisations of Thompson's groups.

math.GR↗

arXiv2014

Cohomological Finiteness Properties of Groups

PhD thesis concerning cohomological finiteness conditions of infinite discrete groups. Much of the material in this thesis has also appeared in arXiv:1311.7629, arXiv:1310.6262, arXiv:1311.6156, and arXiv:1207.1597.

math.GR↗

arXiv2014

Bredon-Poincare Duality Groups

If $G$ is a group which admits a manifold model for $\mathrm{B}G$ then $G$ is a Poincaré duality group. We study a generalisation of Poincaré duality groups, introduced initially by Davis and Leary, motivated by groups $G$ with cocompact manifold models $M$ for $\underline{\mathrm{E}}G$ where $M^H$ is a contractible submanifold for all finite subgroups $H$ of $G$. We give several sources of examples and constructions of these Bredon-Poincaré duality groups, including using the equivariant reflection group trick of Davis and Leary to construct examples of Bredon-Poincaré duality groups arising from actions on manifolds $M$ where the dimensions of the submanifolds $M^H$ are specified. We classify Bredon-Poincaré duality groups in low dimensions, and discuss behaviour under group extensions and graphs of groups.

math.GR↗

arXiv2013

Cohomological finiteness conditions for Mackey and cohomological Mackey functors

We study cohomological finiteness conditions for groups associated to Mackey and cohomological Mackey functors, proving that the cohomological dimension associated to cohomological Mackey functors is always equal to the $\mathcal{F}$-cohomological dimension, and characterising the conditions Mackey-$\mathrm{FP}_n$ and cohomological Mackey-$\mathrm{FP}_n$. We show that all finiteness conditions for cohomological Mackey functors are unchanged when considering only the family of $p$-subgroups, and we characterise cohomological Mackey-$\mathrm{FP}_n$ conditions over the finite field $\mathbb{F}_p$.

math.GR↗

arXiv2013

Centralisers in Houghton's Groups

We study the centralisers of elements, finite subgroups and virtually cyclic subgroups of Houghton's group Hn. We discuss various Bredon (co-)homological finiteness conditions satisfied by Hn including the Bredon (co-)homological dimension and Bredon-FPn conditions, which are analogs of the ordinary co-homological dimension and FPn conditions respectively.

math.GR↗