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An exceptional set in the ergodic theory of rational maps of the Riemann sphere

Published online by Cambridge University Press:  17 April 2001

A. G. ABERCROMBIE
Affiliation:
Department of Pure Mathematics, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK
R. NAIR
Affiliation:
Department of Pure Mathematics, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK

Abstract

A rational map $T$ of degree not less than two is known to preserve a measure, called the conformal measure, equivalent to the Hausdorff measure of the same dimension as its Julia set $J$ and supported there, with respect to which it is ergodic and even exact. As a consequence of Birkhoff's pointwise ergodic theorem almost every $z$ in $J$ with respect to the conformal measure has an orbit that is asymptotically distributed on $J$ with respect to this measure. As a counterpoint to this, the following result is established in this paper. Let $\Omega(z)=\Omega_{T}(z)$ denote the closure of the set $\{T^{n}(z):n=1,2,\ldots\}$. For any expanding rational map $T$ of degree at least two we set \[ S(z_{0})=\{z\in J:z_{0}\not\in \Omega_{T}(z)\}. \] We show that for all $z_{0}$ the Hausdorff dimensions of $S(z)$ and $J$ are equal.

Type
Research Article
Copyright
1997 Cambridge University Press

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