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Entropy for automorphisms of free groups
Authors:Marie Choda
Institution:Department of Mathematics, Osaka Kyoiku University, Asahigaoka, Kashiwara 582-8582, Japan
Abstract:Let $ \sigma $ be the automorphism of the free group $ F_\infty$ which is arising from a permutation of the free generators of $ F_\infty.$ The $ \sigma $ naturally induces the automorphism $ \hat \sigma $ of the reduced $ C^*$-algebra $ C^*_r(F_\infty),$ and also the automorphism $ \bar{\hat \sigma} $ of the group factor $ L(F_\infty).$ We show that the Brown-Germain entropy $ ha(\sigma )$ is zero. This implies that the Brown-Voiculescu topological entropy $ ht(\hat \sigma ),$ the Connes-Narnhofer-Thirring dynamical entropy $ h_\phi (\hat \sigma )$ and the Connes-Størmer entropy $ H(\bar{\hat \sigma} )$ are all zero.

Keywords:Entropy  free group  $C^*$-algebra  amenability
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