Effective SPR conjecture for surface diffeomorphisms

Let ff be a CC^\infty surface diffeomorphism with positive topological entropy. For an ergodic measure μ\mu of ff, write hμ(f)h_\mu(f) for its metric entropy, htop(f)h_{\rm top}(f) for the topological entropy, Lβ0u(f)L^u_{\beta_0}(f) and Lβ0s(f)L^s_{\beta_0}(f) for the sets of points with unstable and stable manifolds of the prescribed uniform size, and Eu(x)E^u(x) and Es(x)E^s(x) for the unstable and stable directions at xx.

Effective SPR conjecture. For every 1>α1>α2>01>\alpha_1>\alpha_2>0, there exist β0>0\beta_0>0 and C>0C>0 such that, for every ergodic measure μ\mu of ff satisfying

hμ(f)α1htop(f),h_\mu(f)\geq \alpha_1 h_{\rm top}(f),

we have

μ(Lβ0u(f)Lβ0s(f){x:(Eu(x),Es(x))>C})>α2.\mu\Big(L^u_{\beta_0}(f)\cap L^s_{\beta_0}(f)\cap\big\{x:\angle\big(E^u(x),E^s(x)\big)>C\big\}\Big)>\alpha_2.

This is expected to strengthen the preceding theorem, which proves the corresponding conclusion with lower bound 2α212\alpha_2-1 under the stronger assumption α2>12\alpha_2>\tfrac12. The conjecture asserts that the same type of uniform stable and unstable control and uniform angle separation should hold for every α2>0\alpha_2>0.

Sources & referencesView supporting material

Primary source

David Burguet, Chiyi Luo and Dawei Yang, “Effective SPR property for surface diffeomorphisms and three-dimensional vector fields”, arXiv:2512.03515 (2025).

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