English

Tame and relatively elliptic $\mathbb{CP}^1$-structures on the thrice-punctured sphere

Geometric Topology 2024-12-25 v2 Differential Geometry

Abstract

Suppose a relatively elliptic representation ρ\rho of the fundamental group of the thrice-punctured sphere SS is given. We prove that all projective structures on SS with holonomy ρ\rho and satisfying a tameness condition at the punctures can be obtained by grafting certain circular triangles. The specific collection of triangles is determined by a natural framing of ρ\rho. In the process, we show that (on a general surface Σ\Sigma of negative Euler characteristics) structures satisfying these conditions can be characterized in terms of their M\"obius completion, and in terms of certain meromorphic quadratic differentials.

Keywords

Cite

@article{arxiv.2107.06370,
  title  = {Tame and relatively elliptic $\mathbb{CP}^1$-structures on the thrice-punctured sphere},
  author = {Samuel A. Ballas and Philip L. Bowers and Alex Casella and Lorenzo Ruffoni},
  journal= {arXiv preprint arXiv:2107.06370},
  year   = {2024}
}

Comments

58 pages, 19 figures, comments welcome. v2: added remarks 3.3.8 and 3.3.9; updated references; fixed minor typos and imprecisions. Final version to appear on Algebraic & Geometric Topology

R2 v1 2026-06-24T04:10:15.642Z