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Large scale properties of groups; growth functions; Dehn functions; small cancellation properties; hyperbolicity and CAT(0); actions and representations; combinatorial group theory; presentations
5
votes
Accepted
Iterated algebraic fibering
Let $G_1$ be the wreath product of $\mathbb{Z}$ with $\mathbb{Z}$. There is a surjective homomorphism $G_1\rightarrow \mathbb{Z}$ whose kernel $G_2$ is isomorphic to $G_1$. This gives a sequence of …
4
votes
Decidability of word problem for group admitting certain action
Is there an algorithm to distinguish the elements of the set $S$? If so, here is a word problem algorithm. This doesn't seem to use any transitivity properties, just faithfulness.
Start with the pos …
5
votes
Topological interpretation for groups of type $FP_2$
It is true that a group $G$ is $FP_2$ if and only if $G$ acts freely cellularly on a connected CW-complex with trivial first homology group. I see from the comments that you are worried about finite …
3
votes
What is the minimal dimension of a complex realising a group representation?
This does not answer Greg's question, but it is related. You can realize any $\mathbb{Z}G$-module you that like as $H_1$ of a based 2-complex, or as $H_2$ of a 3-complex if you insist that the comple …
14
votes
Accepted
Translation lengths in CAT(0) spaces
Consider the following two transformations of $\mathbb{R}^3$: $a:(x,y,z)\mapsto (x+1,y,z)$ and $b:(x,y,z)\mapsto (-x,-y,z+1)$. The translation axis for $a^nb$ is the line $x=n/2$, $y=0$ and $a^nb$ t …
3
votes
Groups acting on products of hyperbolic spaces
This question for a product of one Gromov hyperbolic space is a famous open problem (see for example Bestvina's problem list) and as far as I am aware the general case is also open.
2
votes
Geometric intuition behind Garside's paper?
If you add the relations that the standard generators have order two, then instead of getting the braid group on $n$ strands, you get the symmetric group on $n$ symbols. The generator that correspond …
6
votes
Is there a finitely presented group with infinite homology over $\mathbb{Q}$?
This answers the other part of your question, not answered by Thompson's group. For each $i\geq 3$ there is a finitely presented group $G_i$ with the property that $H_i(G_i\mathbb{Q})$ is infinite di …
8
votes
Accepted
Status of the Hopf-Thurston sign conjecture in dimension 4
There has been a lot of work on cases of this conjecture connected to Coxeter groups. M. Davis and R. Charney made a conjecture that comes from these cases in 1995 in The Euler characteristic of a no …
11
votes
Accepted
Non-finitely presented FP groups with cohomological dimension $2$
The Bestvina-Brady construction of non-finitely presented groups of type FP produces groups of cohomological dimension two. Bestvina-Brady groups are parametrized by finite flag simplicial complexes. …