Finite-Regularity Counterexamples to Katok's Periodic-Point Conjecture

Abstract

For any $r>1$ and any nonnegative sequence $ω(n)=o(n)$, we construct a $C^r$ sphere diffeomorphism $f$ with $h=h_{\mathrm{top}}(f)>0$ such that \begin{equation*} \lim_{n\to\infty}\frac1n\log\#\Fix(f^n)=h, \qquad \sum_{n\geqslant1}e^{-hn+ω(n)}\#\Fix(f^n)<\infty. \end{equation*} Every ergodic invariant probability measure is hyperbolic, and, apart from finitely many fixed points, all periodic points lie in a single topologically mixing homoclinic class of entropy $h$. This shows that the logarithmic periodic-point lower bound is optimal in finite regularity. In particular, we answer the finite-regularity case of Katok&#39;s periodic-point question in the negative.