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Mar 4, 2013 at 8:43 vote accept Dieter
Mar 4, 2013 at 8:43
Mar 4, 2013 at 8:41 comment added Dieter Thanks, this is a very nice answer. Together with Lee Mosher's answer it provides a full answer to my question, i.e. both positive and negative examples. I would like to accept them both, but since this is impossible I will accept Lee Mosher's answer because it was first.
Mar 2, 2013 at 22:51 history edited Misha CC BY-SA 3.0
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Mar 2, 2013 at 21:39 history edited Misha CC BY-SA 3.0
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Mar 2, 2013 at 21:25 comment added Igor Belegradek Oh, the reference is to "Hyperbolic groups with low-dimensional boundary" not to "Geometry of quasi-planes"; sorry I got confused
Mar 2, 2013 at 21:13 comment added Misha Igor, pages in pdf file for some reason do not show up, but it is p. 37-38, after Lemma 3.9. The link is correct. If you prefer archive version arxiv.org/pdf/math/9911003.pdf, it is on pages 41-43. Concerning your 1st question: The result is indeed stated for coarse PD(3) spaces, which does not include contractible 3-manifolds which are not uniformly acyclic. However, if you go through the proof(s), you realize that the proof takes place in a certain metric neighborhood of the group orbit, so the uniform acyclicity assumption can be weakened.
Mar 2, 2013 at 20:36 comment added Igor Belegradek In fact, the reference points to "Geometry of quasi-planes". Could you give a page reference?
Mar 2, 2013 at 20:18 comment added Igor Belegradek Misha, where do you prove that "$\tilde\Gamma$ cannot act properly discontinuously on any contractible 3-manifold"? I only found a proof that $\tilde\Gamma$ cannot act on a coarse PD(3) space (such as the universal cover of a compact aspherical 3-manifold). Of course, for your application you just need to show that $\tilde\Gamma$ cannot act properly discontinuously on the hyperbolic $3$-space, so for the example at hand everything works.
Mar 2, 2013 at 17:33 history answered Misha CC BY-SA 3.0