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BY-NC-ND 3.0 license Open Access Published by De Gruyter Open Access December 22, 2012

Geometry and dynamics of admissible metrics in measure spaces

Anatoly Vershik, Pavel Zatitskiy and Fedor Petrov
From the journal Open Mathematics


We study a wide class of metrics in a Lebesgue space, namely the class of so-called admissible metrics. We consider the cone of admissible metrics, introduce a special norm in it, prove compactness criteria, define the ɛ-entropy of a measure space with an admissible metric, etc. These notions and related results are applied to the theory of transformations with invariant measure; namely, we study the asymptotic properties of orbits in the cone of admissible metrics with respect to a given transformation or a group of transformations. The main result of this paper is a new discreteness criterion for the spectrum of an ergodic transformation: we prove that the spectrum is discrete if and only if the ɛ-entropy of the averages of some (and hence any) admissible metric over its trajectory is uniformly bounded.

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Published Online: 2012-12-22
Published in Print: 2013-3-1

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This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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