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Starting the study of outer length billiards

Luca Baracco, Olga Bernardi and Corentin Fierobe

Vol. 339 (2025), No. 2, 201–222
Abstract

We focus on outer length billiard dynamics, acting on the exterior of a strictly convex planar domain. We first show that ellipses are totally integrable. We then provide an explicit representation of first order terms for the formal Taylor expansion of the corresponding Mather’s β-function. Finally, we provide explicit Lazutkin coordinates up to order 4.

Keywords
monotone twist maps, mathematical billiards, Mather beta function, geometric approximations
Mathematical Subject Classification
Primary: 37E40
Secondary: 37C83
Milestones
Received: 8 May 2025
Revised: 8 September 2025
Accepted: 8 September 2025
Published: 21 September 2025
Authors
Luca Baracco
University of Padova
Italy
Olga Bernardi
University of Padova
Italy
Corentin Fierobe
University of Rome “Tor Vergata”
Italy

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