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Selim Ghazouani

Publications and source records attributed to Selim Ghazouani.

15 recordsLinked to original sources
arXiv2026

Spectrum of SL(2,R)-characters: the once-punctured torus case

Consider a topological surface $Σ$. We introduce the spectrum of a representation from the fundamental group of $Σ$ to SL(2,R), which is a subset of projective measured lamination on the surface, which captures the directions along which the representation fails to be Fuchsian, and which characterizes the action of the mapping class group on this representation. In the case of the once-punctured torus, we show that the spectrum of a generic representation is a Cantor set, and that it completely describes the dynamics of the familly of locally constant cocycles above interval exchange transformations associated to the representation.

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arXiv2024

Closed geodesics in dilation surfaces

We prove that directions of closed geodesics in every dilation surface form a dense subset of the circle. The proof draws on a study of the degenerations of the Delaunay triangulation of dilation surfaces under the action of Teichmüller flow in the moduli space.

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arXiv2023

Regularity of conjugacies of linearizable generalized interval exchange transformations

We consider generalized interval exchange transformations (GIETs) of d intervals ($d\geq 2$) which are linearizable, i.e. differentiably conjugated to standard interval exchange maps (IETs) via a diffeomorphism h of [0, 1] and study the regularity of the conjugacy h. Using a renormalisation operator obtained accelerating Rauzy-Veech induction, we show that, under a full measure condition on the IET obtained by linearization, if the orbit of the GIET under renormalisation converges exponentially fast in a $C^2$ distance to the subspace of IETs, there exists an exponent $0 < α< 1$ such that h is $C^{1+α}$. Combined with the results proved by the authors in [4], this implies in particular the following improvement of the rigidity result in genus two proved in previous work by the same authors (from $C^1$ to $C^{1+α}$ rigidity): for almost every irreducible IET $T_0$ with d = 4 or d = 5, for any GIET which is topologically conjugate to $T_0$ via a homeomorphism h and has vanishing boundary, the topological conjugacy h is actually a $C^{1+α}$ diffeomorphism, i.e. a diffeomorphism h with derivative Dh which is $α$-Hölder continuous.

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arXiv2021

A priori bounds for GIETs, affine shadows and rigidity of foliations in genus 2

We prove a rigidity result for foliations on surfaces of genus two, which can be seen as a generalization to higher genus of Herman's theorem on circle diffeomorphisms and, correspondingly, flows on the torus. We prove in particular that, if a smooth, orientable foliation with non-degenerate (Morse) singularities on a closed surface of genus two is minimal, then, under a full measure condition for the rotation number, it is differentiably conjugate to a linear foliation. The corresponding result at the level of Poincaré sections is that, for a full measure set of interval exchange transformations with 4 or 5 continuity intervals and irreducible combinatorics, any generalized interval exchange transformation which is topologically conjugate to a IET from this set and satisfies an obstruction given by a boundary operator is $\mathcal{C}^1$-conjugate to it. This in particular settles a conjecture by Marmi, Moussa and Yoccoz in genus two. Our results also show that this conjecture on the rigidity of GIETs can be reduced to the study of affine IETs, or more precisely of Birkhoff sums of piecewise constant observables over standard IETs, in genus $g \geq 3$. Our approach is via renormalization, namely we exploit a suitable Oseledets regular acceleration of the Rauzy-Veech induction on the space of GIETs. For infinitely renormalizable, irrational GIETs of any number of intervals $d\geq 2$ we prove a dynamical dichotomy on the behaviour of the orbits under renormalization, by proving that either an orbit is recurrent to certain bounded sets in the space of GIETs, or it diverges and it is approximated (up to lower order terms) by the orbit of an affine IET (a case that we refer to as affine shadowing).

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arXiv2020

Local rigidity for periodic generalised interval exchange transformations

In this article we study local rigidity properties of generalised interval exchange maps using renormalisation methods. We study the dynamics of the renormalisation operator $\mathcal{R}$ acting on the space of $\mathcal{C}^{3}$-generalised interval exchange transformations at fixed points (which are standard periodic type IETs). We show that $\mathcal{R}$ is hyperbolic and that the number of unstable direction is exactly that predicted by the ergodic theory of IETs and the work of Forni and Marmi-Moussa-Yoccoz. As a consequence we prove that the local $\mathcal{C}^1$-conjugacy class of a periodic interval exchange transformation, with $d$ intervals, whose associated surface has genus $g$ and whose Lyapounoff exponents are all non zero is a codimension $g-1 +d-1$ $\mathcal{C}^1$-submanifold of the space of $\mathcal{C}^{3}$-generalised interval exchange transformations. This solves a particular case of a conjecture of Marmi-Moussa-Yoccoz.

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arXiv2019

The symplectic structure of renormalisation of circle diffeomorphisms with breaks

In this article we prove that iterated renormalisations of $\mathcal{C}^r$ circle diffeomorphisms with $d$ breaks, $r>2$, with given size of breaks, converge to an invariant family of piecewise Moebius maps, of dimension $2d$. We prove that this invariant family identifies with a \textit{relative character variety} $χ(π_1 Σ, \mathrm{PSL}(2,\mathbb{R}), \mathbf{h})$ where $Σ$ is a $d$-holed torus, and that the renormalisation operator identifies with a sub-action of the mapping class group $\mathrm{MCG}(Σ)$. This action is known to preserves a symplectic form, thanks to the work of Guruprasad-Huebschmann-Jeffrey-Weinstein. Its pull-back through the aforementioned identification provides a symplectic form invariant by renormalisation.

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arXiv2019

Une invitation aux surfaces de dilatation

This text is an introduction to dilation surfaces. We attempt to expose some geometric and dynamical aspects of the subject: moduli spaces, directional foliations and the Teichmüller flow.

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arXiv2019

Cascades in the dynamics of affine interval exchange transformations

We describe in this article the dynamics of a $1$-parameter family of affine interval exchange transformations. It amounts to studying the directional foliations of a particular affine surface, the Disco surface. We show that this family displays various dynamical behaviours: it is generically dynamically trivial, but for a Cantor set of parameters the leaves of the foliations accumulate to a (transversely) Cantor set. s study is achieved through the analysis the dynamics of the Veech group of this surface combined a modified version of Rauzy induction in the context of affine interval exchange transformations.

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arXiv2018

Teichmüller dynamics, dilation tori and piecewise affine circle homeomorphisms

We study the coarse geometry of the moduli space of dilation tori with two singularities and the dynamical properties of the action of the Teichmuller flow on this moduli space. This leads to a proof that the vertical foliation of a dilation torus is almost always Morse-Smale. As a corollary, we get that the generic piecewise affine circle homeomorphism with two break points -with respect to the Lebesgue measure- is Morse-Smale.

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arXiv2017

Moduli spaces of flat tori with prescribed holonomy

We generalise to the genus one case several results of Thurston concerning moduli spaces of flat Euclidean structures with conical singularities on the two dimensional sphere. More precisely, we study the moduli space of flat tori with $n$ cone points and a prescribed holonomy $ρ$. In his paper `Flat Surfaces' Veech has established that under some assumptions on the cone angles, such a moduli space ${\mathcal{F}}_{[ρ]}\subset \mathscr M_{1,n}$ carries a natural geometric structure modeled on the complex hyperbolic space ${\mathbb C}{\mathbb{H} }^{n-1}$ which is not metrically complete. Using surgeries for flat surfaces, we prove that the metric completion $\overline{\mathcal{F}_{[ρ]}}$ is obtained by adjoining to $ {\mathcal{F}}_{[ρ]} $ certain strata that are themselves moduli spaces of flat surfaces of genus 0 or 1, obtained as degenerations of the flat tori whose moduli space is $ {\mathcal{F}}_{[ρ]}$. We show that the ${\mathbb C}{\mathbb{H} }^{n-1}$-structure of $ {\mathcal{F}}_{[ρ]}$ extends to a complex hyperbolic cone-manifold structure of finite volume on $ \overline{\mathcal{F}_{[ρ]}}$ and we compute the cone angles associated to the different strata of codimension 1. Finally, we address the question of whether or not the holonomy of Veech's ${\mathbb C}{\mathbb{H} }^{n-1}$-structure on $ \mathcal F_ρ$ has a discrete image in $ {\rm Aut}({\mathbb C}{\mathbb{H} }^{n-1})=\mathrm{PU}(1,n-1)$. We outline a general strategy to find moduli spaces $\mathcal F_{[ρ]}$ whose ${\mathbb C}{\mathbb{H} }^{n-1}$-holonomy gives rise to lattices in $\mathrm{PU}(1,n-1)$ and eventually we give a finite list of $\mathcal F_{[ρ]}$'s whose holonomy is a complex hyperbolic arithmetic lattice.

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arXiv2016

Affine surfaces and their Veech groups

We introduce a class of objects which we call 'affine surfaces'. These provide families of foliations on surfaces whose dynamics we are interested in. We present and analyze a couple of examples, and we define concepts related to these in order to motivate several questions and open problems. In particular we generalise the notion of Veech group to affine surfaces, and we prove a structure result about these Veech groups.

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arXiv2016

Moduli spaces of flat tori and elliptic hypergeometric functions

In the genus one case, we make explicit some constructions of Veech on flat surfaces and generalize some geometric results of Thurston about moduli spaces of flat spheres as well as some equivalent ones but of an analytico-cohomological nature of Deligne-Mostow, which concern the monodromy of Appell-Lauricella hypergeometric functions. In the twin paper arXiv:1604.01812, we follow Thurston's approach and study moduli spaces of flat tori with conical singularities and prescribed holonomy by means of geometrical methods relying on surgeries for flat surfaces. In the present paper, we study the same objects making use of analytical and cohomological methods, more in the spirit of Deligne-Mostow's paper.

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arXiv2016

Mapping class group dynamics and the holonomy of branched affine structures

We classify, up to few exceptions, the orbit closures of the $\mathrm{Mod}(Σ)$-action on the affine character variety $χ(\mathrm{Aff}(\mathbb{C}))$. We obtain from this classification that the only obstruction for a non-abelian representation $ρ: π_1 Σ\longrightarrow \mathrm{Aff}(\mathbb{C})$ to be the holonomy of a branched affine structure on $Σ$ is to be Euclidean and not to have positive volume, where $Σ$ is a closed oriented surface of genus $g \geq 2$.

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arXiv2015

Mapping class group dynamics on Aff(C)-characters

We prove that in genus bigger than $2$, the mapping class group action on $\mathrm{Aff}(\mathbb{C})$-characters is ergodic. This implies that almost every representation $π_1 S \longrightarrow \mathrm{Aff}(\mathbb{C})$ is the holonomy of a branched affine structure on $S$, where $S$ is a closed orientable surface of genus $g \geq 2$.

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