Fractal representation of the attractive lamination of an automorphism of the free group
Annales de l'Institut Fourier, Volume 56 (2006) no. 7, pp. 2161-2212.

In this paper, we extend to automorphisms of free groups some results and constructions that classically hold for morphisms of the free monoid, i.e., the so-called substitutions. A geometric representation of the attractive lamination of a class of automorphisms of the free group (irreducible with irreducible powers (iwip) automorphisms) is given in the case where the dilation coefficient of the automorphism is a unit Pisot number. The shift map associated with the attractive symbolic lamination is, in this case, proved to be measure-theoretically isomorphic to a domain exchange on a self-similar Euclidean compact set. This set is called the central tile of the automorphism, and is inspired by Rauzy fractals associated with Pisot primitive substitutions. The central tile admits some specific symmetries, and is conjectured under the Pisot hypothesis to be a fundamental domain for a toral translation.

Nous étendons aux automorphismes de groupes libres certains résultats et constructions associés aux morphismes de monoïdes libres, autrement appelés substitutions. Nous construisons une représentation géométrique de la lamination attractive d’une classe d’automorphismes du groupe libre (plus précisément, les automorphismes irréductibles et dont les puissances sont irréductibles) dans le cas où le coefficient de dilatation de l’automorphisme est un nombre de Pisot unitaire. On montre que, dans ce cas, l’application de décalage sur la lamination symbolique attractive est isomorphe en mesure à un échange de domaines sur un ensemble autosimilaire compact. Cet ensemble est appelé tuile centrale de l’automorphisme ; sa construction s’inspire des fractals de Rauzy associés à une substitution primitive Pisot. La tuile centrale admet des symétries liées à l’inversion dans le groupe libre. On conjecture dans le cas général que la tuile centrale est un domaine fondamental pour une translation sur un groupe compact.

DOI: 10.5802/aif.2237
Classification: 20E05, 37B10, 05B45, 68R15
Keywords: Free group automorphism, attractive lamination, substitution, symbolic $\quad $ dynamics, self-similarity, Pisot number
Keywords: automorphisme du groupe libre, lamination attractive, substitution, dynamique symbolique, auto-similarité, Pisot number
Arnoux, Pierre 1; Berthé, Valérie 2; Hilion, Arnaud 3; Siegel, Anne 4

1 IML-UMR 6206 163 avenue de Luminy Case 907 13288 Marseille cedex 9 (France)
2 Université de Montpellier II LIRMM-CNRS UMR 5506 161 rue Ada 34392 Montpellier cedex 5 (France)
3 Université Aix-Marseille III LATP Avenue de l’escadrille Normandie-Niémen Case A 13397 Marseille cedex 20 (France)
4 IRISA-CNRS Campus de Beaulieu 35042 Rennes cedex (France)
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Arnoux, Pierre; Berthé, Valérie; Hilion, Arnaud; Siegel, Anne. Fractal representation of the attractive lamination of an automorphism of the free group. Annales de l'Institut Fourier, Volume 56 (2006) no. 7, pp. 2161-2212. doi : 10.5802/aif.2237.

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