On fast Birkhoff averaging
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Abstract
We study the pointwise behavior of Birkhoff sums S(n)phi(x) on subshifts of finite type for Holder continuous functions phi. In particular, we show that for a given equilibrium state mu associated to a Holder continuous potential, there are points x such that S(n)phi(x)  nE(mu)phi similar to an(beta) for any a > 0 and 0 < beta < 1. Actually the Hausdorff dimension of the set of such points is bounded from below by the dimension of mu and it is attained by some maximizing equilibrium state nu such that E(nu)phi = E(mu)phi. On such points the ergodic average n(1) S(n)phi(x) converges more rapidly than predicted by the Birkhoff Theorem, the Law of the Iterated Logarithm and the Central Limit Theorem. All these sets, for different choices (alpha, beta), are distinct but have the same dimension. This reveals a rich multifractal structure of the symbolic dynamics. As a consequence, we prove that the set of uniform recurrent points, which are close to periodic points, has full dimension. Applications are also given to the study of syndetic numbers, HardyWeierstrass functions and lacunary Taylor series.
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Research areas and keywords  Subject classification (UKÄ) – MANDATORY

Original language  English 

Pages (fromto)  443467 
Journal  Mathematical Proceedings of the Cambridge Philosophical Society 
Volume  135 
Issue number  3 
Publication status  Published  2003 
Publication category  Research 
Peerreviewed  Yes 