# Commentarii Mathematici Helvetici

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**Volume 76, Issue 2, 2001, pp. 300–313**

**DOI: 10.1007/PL00000380**

Published online: 2001-06-30

Hyperbolic 3-manifolds as cyclic branched coverings

M. Reni and Bruno Zimmermann^{[1]}(1) Università degli Studi di Trieste, Italy

There is an extensive literature on the characterization of knots in the 3-sphere which have the same 3-manifold as a common n-fold cyclic branched covering, for some integer $ n \ge 2 $. In the present paper, we study the following more general situation. Given two integers m and n, how are knots K1 and K2 related such that the m-fold cyclic branched covering of K1 coincides with the n-fold cyclic branched covering of K2. Or, seen from the point of view of 3-manifolds: in how many different ways can a given 3-manifold occur as a cyclic branched covering of knots in S3. Under certain hypotheses, we solve this problem for the basic class of hyperbolic 3-manifolds and hyperbolic knots (the other basic class is that of Seifert fiber spaces resp. of torus and Montesinos knots for which the situation is well understood; the general case can then be analyzed using the equivariant sphere and torus decomposition into Seifert fiber spaces and hyperbolic manifolds).

*Keywords: * Hyperbolic knot, cyclic branched covering, hyperbolic 3-manifold

Reni M., Zimmermann Bruno: Hyperbolic 3-manifolds as cyclic branched coverings. *Comment. Math. Helv.* 76 (2001), 300-313. doi: 10.1007/PL00000380