Katok's exponential periodic-orbit growth conjecture for surface diffeomorphisms

Let MM be a compact surface, let f ⁣:MMf\colon M\to M be a diffeomorphism, let Pn(f)={xM:x=fn(x)}P_n(f)=\{x\in M:x=f^n(x)\}, and let htop(f)h_{\operatorname{top}}(f) denote the topological entropy of ff. Katok's conjecture. Is it true that

lim supn+Pn(f)enhtop(f)>0?\limsup_{n\to +\infty}\frac{\sharp P_n(f)}{e^{n h_{\operatorname{top}}(f)}}>0?

for any (i) CrC^r (r>1r>1) or (ii) CC^\infty diffeomorphism ff of a compact surface? The conjecture asks for an exponential lower-growth estimate for periodic orbits at the topological entropy scale; the source does not state whether it has been resolved.

Sources & referencesView supporting material

Primary source

Gang Liao and Jing Wei, “Metric entropy and homoclinic growth rate”, arXiv:2511.08227 (2025).

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