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Distortion bounds for $C^{2+η}$ unimodal maps

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Todd M.

Fundamenta Mathematicae

2007

tom 193

nr 1

37-77

We obtain estimates for derivative and cross-ratio distortion for $C^{2+η}$ (any η > 0) unimodal maps with non-flat critical points. We do not require any "Schwarzian-like" condition. For two intervals J ⊂ T, the cross-ratio is defined as the value B(T,J): = (|T| |J|)/(|L| |R|) where L,R are the left and right connected components of T∖J respectively. For an interval map g such that $g_T: T → ℝ$ is a diffeomorphism, we consider the cross-ratio distortion to be B(g,T,J): = B(g(T),g(J))/B(T,J). We prove that for all 0 < K < 1 there exists some interval I₀ around the critical point such that for any intervals J ⊂ T, if $fⁿ|_T$ is a diffeomorphism and fⁿ(T) ⊂ I₀ then B(fⁿ,T,J) > K. Then the distortion of derivatives of $fⁿ|_J$ can be estimated with the Koebe lemma in terms of K and B(fⁿ(T),fⁿ(J)). This tool is commonly used to study topological, geometric and ergodic properties of f. Our result extends one of Kozlovski.

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1 Fundamenta Mathematicae

1 Todd M.

1 2007

Wyniki wyszukiwania

Distortion bounds for $C^{2+η}$ unimodal maps