English

Non-injective representations of a closed surface group into $PSL(2,\mathbb R)$

Geometric Topology 2016-07-06 v1 Differential Geometry

Abstract

Let ee denote the Euler class on the space Hom(Γg,PSL(2,R))Hom(\Gamma_g, PSL(2,\mathbb R)) of representations of the fundamental group Γg\Gamma_g of the closed surface Σg\Sigma_g of genus gg. Goldman showed that the connected components of Hom(Γg,PSL(2,R))Hom(\Gamma_g, PSL(2,\mathbb R)) are precisely the inverse images e1(k)e^{-1}(k), for 22gk2g22-2g\leq k\leq 2g-2, and that the components of Euler class 22g2-2g and 2g22g-2 consist of the injective representations whose image is a discrete subgroup of PSL(2,R)PSL(2,\mathbb R). We prove that non-faithful representations are dense in all the other components. We show that the image of a discrete representation essentially determines its Euler class. Moreover, we show that for every genus and possible corresponding Euler class, there exist discrete representations.

Keywords

Cite

@article{arxiv.math/0502585,
  title  = {Non-injective representations of a closed surface group into $PSL(2,\mathbb R)$},
  author = {Louis Funar and Maxime Wolff},
  journal= {arXiv preprint arXiv:math/0502585},
  year   = {2016}
}

Comments

15 pages, 2 figures

R2 v1 2026-07-22T17:16:11.294Z