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Pre-printDate
2016-10-01Author
Dowdall, SKapovich, I
Taylor, SJ
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http://hdl.handle.net/20.500.12613/5014
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10.1007/s11856-016-1426-2Abstract
© 2016, Hebrew University of Jerusalem. This paper gives a detailed analysis of the Cannon–Thurston maps associated to a general class of hyperbolic free group extensions. Let F denote a free group of finite rank at least 3 and consider a convex cocompact subgroup Γ ≤ Out(F), i.e. one for which the orbit map from Γ into the free factor complex of F is a quasi-isometric embedding. The subgroup Γ determines an extension EΓof F, and the main theorem of Dowdall–Taylor [DT14] states that in this situation EΓis hyperbolic if and only if Γ is purely atoroidal. Here, we give an explicit geometric description of the Cannon–Thurston maps ∂F → ∂EΓfor these hyperbolic free group extensions, the existence of which follows from a general result of Mitra. In particular, we obtain a uniform bound on the multiplicity of the Cannon–Thurston map, showing that this map has multiplicity at most 2 rank(F). This theorem generalizes the main result of Kapovich and Lustig [KL15] which treats the special case where Γ is infinite cyclic. We also answer a question of Mahan Mitra by producing an explicit example of a hyperbolic free group extension for which the natural map from the boundary of Γ to the space of laminations of the free group (with the Chabauty topology) is not continuous.Citation to related work
Springer Science and Business Media LLCHas part
Israel Journal of MathematicsADA compliance
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http://dx.doi.org/10.34944/dspace/4996