Sharpness of the entropy threshold for infinitely many ergodic measures of maximal entropy

Let ff be a CrC^r diffeomorphism of a closed surface, where 1<r<1<r<\infty, and let λmin(f)\lambda_{\min}(f) denote the minimum expansion rate appearing in the entropy estimates. A measure maximizing entropy is a measure bcbc with h(f,μ)=htop(f)h(f,\mu)=h_{\operatorname{top}}(f); it is ergodic when it is ergodic for ff. Sharpness conjecture. For any ε>0\varepsilon>0 and any 1<r<1<r<\infty, there is a CrC^r surface diffeomorphism ff with

htop(f)>λmin(f)rεh_{\operatorname{top}}(f)>\frac{\lambda_{\min}(f)}r-\varepsilon

and infinitely many ergodic measures maximizing entropy. This would show that the threshold in the finiteness theorem is sharp; the conjecture remains open.

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Primary source

Jérôme Buzzi, Sylvain Crovisier and Omri Sarig, “Measures of maximal entropy for surface diffeomorphisms”, arXiv:1811.02240 (2019).

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