Pentagon representations and complex projective structures on closed surfaces
[Représentations pentagones et structures projectives complexes sur les surfaces fermées]
Annales de l'Institut Fourier, Tome 73 (2023) no. 1, pp. 423-445.

Nous définissons une classe de représentations du groupe fondamental d’une surface fermée de genre 2 dans PSL 2 ()  : les représentations pentagones. Nous montrons que ce sont exactement les représentations d’un groupe de surface dans PSL 2 () qui n’admettent pas de décomposition de Schottky, i.e. de décomposition en pantalons telle que la restriction de la représentation à chaque pantalon est un isomorphisme sur un groupe de Schottky. Ce faisant, nous exhibons une lacune dans la preuve de Gallo, Kapovich et Marden du fait que toute représentation non-élémentaire d’un groupe de surface dans PSL 2 () est l’holonomie d’une structure projective, avec éventuellement un point de branchement d’ordre 2. Nous montrons que les représentations pentagones sont de telles holonomies et réparons leur preuve.

We define a class of representations of the fundamental group of a closed surface of genus 2 to PSL 2 (): the pentagon representations. We show that they are exactly the non-elementary PSL 2 ()-representations of surface groups that do not admit a Schottky decomposition, i.e. a pants decomposition such that the restriction of the representation to each pair of pants is an isomorphism onto a Schottky group. In doing so, we exhibit a gap in the proof of Gallo, Kapovich and Marden that every non-elementary representation of a surface group to PSL 2 () is the holonomy of a projective structure, possibly with one branched point of order 2. We show that pentagon representations arise as such holonomies and repair their proof.

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DOI : 10.5802/aif.3528
Classification : 57M50
Keywords: Projective structure, holonomy, surface groups representations.
Mot clés : Structure projective, holonomie, représentations de groupes de surfaces.
Le Fils, Thomas 1

1 Institut de Mathématiques de Jussieu Paris Rive Gauche (IMJ-PRG) 75005 Paris (France)
Licence : CC-BY-ND 4.0
Droits d'auteur : Les auteurs conservent leurs droits
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Le Fils, Thomas. Pentagon representations and complex projective structures on closed surfaces. Annales de l'Institut Fourier, Tome 73 (2023) no. 1, pp. 423-445. doi : 10.5802/aif.3528. https://aif.centre-mersenne.org/articles/10.5802/aif.3528/

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