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21
votes
Fundamental groups of closed hyperbolic 3-manifolds are freely indecomposable
One can also see it using the theory of ends. If $\pi_1M$ were freely decomposable, then it would follow from the easy direction of Stallings' Ends Theorem that $\pi_1M$ had two or infinitely many en …
20
votes
〈x,y : x^p = y^p = (xy)^p = 1〉
Your group is the fundamental group of a 2-dimensional orbifold with underlying surface the 2-sphere and 3 cone points of order p. It follows that it acts properly discontinuously and cocompactly by …
14
votes
Accepted
Topology of boundaries of hyperbolic groups
There are plenty of other possibilities. Here are a few examples:
The boundary of the fundamental group of an acylindrical hyperbolic 3-manifold with totally geodesic boundary is homeomorphic to a S …
13
votes
The work of Thurston
This isn't a direct answer to the actual question, but in your first sentence I think you're alluding to Thurston's article On proof and progress in mathematics. In section 6, entitled "Some persona …
13
votes
Accepted
Virtual fibering conjecture for cusped hyperbolic manifolds
It does hold - Wise proved that finite-volume non-compact hyperbolic 3-manifolds are virtually special, hence virtually RFRS and so virtually fibred by one of Agol's results. Details and references a …
11
votes
Accepted
Examples of 3-manifolds with RFRS fundamental group
Agol's original paper on RFRS gives a nice short proof that the fundamental group of any manifold which also happens to be a finite-index subgroup of your favourite right-angled reflection group is RF …
11
votes
Accepted
Do you know how to construct a compact hyperbolic 3-manifold with three or four totally geod...
Theorem(Long and Niblo): If $M$ is a 3-manifold and $S$ is an incompressible component of $\partial M$ then $\pi_1 S$ is separable in $\pi_1 M$ (pick a base point in $S$ to make sense of this).
This …
8
votes
Accepted
Fundamental groups of hyperbolic $4$-manifolds and $\rm CAT(0)$ cube complexes
This question is certainly open in general. I don't know if anyone has formally expressed an 'expectation' in print, but you might be interested in the following pieces of positive evidence.
I believ …
8
votes
Accepted
Why isn't $\langle x,y,z|xyzx^{-1}y^{-1}z^{-1}\rangle$ a hyperbolic surface group?
I think Lee's and Steve's comments pretty much answer this question. Let me try to summarize, and clear up a couple of misconceptions that seem to be lurking. For convenience, I'll denote your group …
7
votes
Accepted
Hyperbolic knot complement groups and relative dimension
Proposition 9.6 of M. Kapovich's 'Homological dimension and critical exponent of Kleinian groups' (it's Proposition 9.5 of the arXiv version) asserts that the cohomological dimension of the pair $(G,\ …
6
votes
Do quasi convex hyperbolic subgroups remain quasi convex after adding redundant generators?
As this is too long for a comment, I'll post it as an answer.
As you seem to be interested in CAT(0) cube complexes, I want to point out that there is, in fact, a ninth type of quasiconvexity, which …
5
votes
Accepted
Finite covers of hyperbolic surfaces and the `second systole´
[17/4/17: edited to correct proof.]
This is true. First, we need a lemma which builds a related cover. Throughout, $\alpha$ is a simple closed geodesic of length $\ell$, and $\beta_1,\ldots,\beta_n$ …
5
votes
Accepted
Does length spectrum determine a hyperbolic 3-manifold? What if we also know holonomies?
I think your questions are answered by this paper of Leininger, McReynolds, Neumann and Reid. In their terminology, your first question is asking about manifolds with equal length sets, and your seco …
5
votes
Residual finiteness of hyperbolic 3-manifold groups
Sam Nead's answer does it, but perhaps I can offer a slightly different perspective on Question 1. No complicated hyperbolic gluing results are needed.
I assume we are satisfied with the characterisat …
3
votes
Density of ends of long words in a hyperbolic group
This sort of thing was worked out by Coornaert, who constructed Patterson--Sullivan measures on the boundaries of word-hyperbolic groups:
Michel Coornaert, Mesures de Patterson-Sullivan sur le bord d …