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Iterated monodromy groups

Published online by Cambridge University Press:  05 July 2011

Volodymyr Nekrashevych
Texas A&M University, USA
C. M. Campbell
University of St Andrews, Scotland
M. R. Quick
University of St Andrews, Scotland
E. F. Robertson
University of St Andrews, Scotland
C. M. Roney-Dougal
University of St Andrews, Scotland
G. C. Smith
University of Bath
G. Traustason
University of Bath
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The paper is a survey of topics related to the theory of iterated monodromy groups and its applications. We also present a collection of examples illustrating different aspects of the theory.


Iterated monodromy groups are algebraic invariants of topological dynamical systems (e.g., rational functions acting on the Riemann sphere). They encode in a computationally efficient way combinatorial information about the dynamical systems. In hyperbolic (expanding) case the iterated monodromy group contains all essential information about the dynamical system. For instance, the Julia set of the system can be reconstructed from the iterated monodromy group).

Besides their applications to dynamical systems (see, for instance [BN06] and [Nek08b]) iterated monodromy groups are interesting from the point of view of group theory, as they often possess exotic properties. In some sense their complicated structure is parallel to the complicated structure of the associated fractal Julia sets. In some cases the relation with the dynamical systems can be used to understand algebraic properties of the iterated monodromy groups.

Even though the main application of the iterated monodromy groups is dynamics, their origins are in algebra (however, some previous works in holomorphic dynamics contained constructions directly related to the iterated monodromy groups, see [HOV95, LM97, Pil00]). They were defined in 2001 in connection with the following construction due to R. Pink. Let F(x) be a rational function over ℂ.

Publisher: Cambridge University Press
Print publication year: 2011

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