Entropy monotonicity and superstable cycles for the quadratic family revisited

TL;DR

This paper provides a real analysis proof of the monotonicity of topological entropy in quadratic maps, offering a simpler, geometrical approach that also revisits superstable cycles, contrasting with previous complex analysis methods.

Contribution

It introduces a real analysis and geometrical proof of entropy monotonicity for quadratic maps, simplifying previous complex analysis-based proofs and revisiting superstable cycles.

Findings

Proof of entropy monotonicity using real analysis

Geometrical approach based on transverse intersections

Revisit of superstable cycles in quadratic maps

Abstract

The main result of this paper is a proof using real analysis of the monotonicity of the topological entropy for the family of quadratic maps, sometimes called Milnor's Monotonicity Conjecture. In contrast, the existing proofs rely in one way or another on complex analysis. Our proof is based on tools and algorithms previously developed by the authors and collaborators to compute the topological entropy of multimodal maps. Specifically, we use the number of transverse intersections of the map iterates with the so-called critical line. The approach is technically simple and geometrical. The same approach is also used to briefly revisit the superstable cycles of the quadratic maps, since both topics are closely related.