We prove that infinite mapping class group orbits are dense in the character variety of Deroin–Tholozan representations. In other words, the action is minimal except for finite orbits. Our arguments rely on the symplectic structure of the character variety, emphasizing this geometric perspective over its algebraic properties.
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Figure 9. In black: the $ i^\mathrm{th} $ and $ (i+1)^\mathrm{th} $ triangles in the $ \mathscr{B} $-triangle chain of $ [\rho] $. In mauve: the first triangle in the $ \mathscr{D}_i $-triangle chain of $ [\rho] $. In purple: the $ i^\mathrm{th} $ triangle in the $ \mathscr{E}_i $-triangle chain of $ [\rho] $
| [1] |
R. L. Benedetto and W. M. Goldman, The topology of the relative character varieties of a quadruply-punctured sphere, Experiment. Math., 8 (1999), 85-103.
doi: 10.1080/10586458.1999.10504391.
|
| [2] |
P. Boalch, From Klein to Painlevé via Fourier, Laplace and Jimbo, Proc. Lond. Math. Soc. (3), 90 (2005), 167-208.
doi: 10.1112/S0024611504015011.
|
| [3] |
P. Boalch, Some explicit solutions to the Riemann-Hilbert problem, in Differential Equations and Quantum Groups, 85-112, IRMA Lect. Math. Theor. Phys., vol. 9, European Mathematical Society (EMS), Zürich, 2007.
doi: 10.4171/020-1/6.
|
| [4] |
Y. Bouilly and G. Faraco, Modular orbits on the representation spaces of compact abelian Lie groups, Groups Geom. Dyn., 17 (2023), 719-749.
doi: 10.4171/ggd/716.
|
| [5] |
S. Bronstein and A. Maret, Tykhyy's conjecture on finite mapping class group orbits, preprint, arXiv: 2409.04379v2, 2024.
|
| [6] |
S. Cantat, C. Dupont and F. Martin-Baillon, Dynamics on Markov surfaces: Classification of stationary measures, preprint, arXiv: 2404.01721v1, 2024.
|
| [7] |
S. Cantat and F. Loray, Dynamics on character varieties and Malgrange irreducibility of Painlevé Ⅵ equation, Ann. Inst., Fourier, 59 (2009), 2927-2978.
doi: 10.5802/aif.2512.
|
| [8] |
B. Deroin and N. Tholozan, Supra-maximal representations from fundamental groups of punctured spheres to $\text{PSL}(2, {\mathbb R})$, Ann. Sci. Éc. Norm. Supér. (4), 52 (2019), 1305-1329.
doi: 10.24033/asens.2410.
|
| [9] |
B. Farb and D. Margalit, A Primer on Mapping Class Groups, Princeton Mathematical Series, 49, Princeton University Press, Princeton, NJ, 2012.
|
| [10] |
A. Fenyes and A. Maret, The geometry of deroin-tholozan representations, preprint, arXiv: 2312.09199v3, 2023.
|
| [11] |
W. M. Goldman, The symplectic nature of fundamental groups of surfaces, Adv. Math., 54 (1984), 200-225.
doi: 10.1016/0001-8708(84)90040-9.
|
| [12] |
W. M. Goldman, Invariant functions on Lie groups and Hamiltonian flows of surface group representations, Invent. Math., 85 (1986), 263-302.
doi: 10.1007/BF01389091.
|
| [13] |
W. M. Goldman, Ergodic theory on moduli spaces, Ann. Math. (2), 146 (1997), 475-507.
doi: 10.2307/2952454.
|
| [14] |
W. M. Goldman, The modular group action on real SL(2)-characters of a one-holed torus, Geom. Topol., 7 (2003), 443-486.
doi: 10.2140/gt.2003.7.443.
|
| [15] |
W. M. Goldman, Mapping class group dynamics on surface group representations, in Problems on Mapping Class Groups and Related Topics, 189-214, Proc. Sympos. Pure Math., vol. 74, American Mathematical Society, Providence, RI, 2006.
doi: 10.1090/pspum/074/2264541.
|
| [16] |
W. M. Goldman, S. Lawton and E. Z. Xia, The mapping class group action on ${\rm{SU}}(3)$-character varieties, Ergodic Theory Dynam. Systems, 41 (2021), 2382-2396.
doi: 10.1017/etds.2020.50.
|
| [17] |
W. M. Goldman and E. Z. Xia, Ergodicity of mapping class group actions on SU(2)-character varieties, in Geometry, Rigidity, and Group Actions, 591-608, University of Chicago Press, 2011.
|
| [18] |
A. S. Golsefidy and N. Tamam, Closure of orbits of the pure mapping class group in the character variety, Proc. Natl. Acad. Sci. USA, 122 (2025), Paper No. e2416120122, 10 pp.
doi: 10.1073/pnas.2416120122.
|
| [19] |
A. V. Kitaev, Remarks towards a classification of RS42(3)-transformations and algebraic solutions of the sixth Painlevé equation, in Théories Asymptotiques et Équations de Painlevé, 199-227, Sémin. Congr., vol. 14, Société Mathématique de France, Paris, 2006.
|
| [20] |
J. Marché and M. Wolff, The modular action on $\mathrm{PSL}_2(\mathbb{R})$-characters in genus 2, Duke Math. J., 165 (2016), 371-412.
doi: 10.1215/00127094-3166522.
|
| [21] |
A. Maret, Ergodicity of the mapping class group action on Deroin-Tholozan representations, Groups Geom. Dyn., 16 (2022), 1341-1368.
doi: 10.4171/ggd/695.
|
| [22] |
A. Maret, Action-angle coordinates for surface group representations in genus zero, J. Symplectic Geom., 22 (2024), 937-999.
doi: 10.4310/JSG.241101002149.
|
| [23] |
G. Mondello, Topology of representation spaces of surface groups in ${\rm{PSL}} _2(\mathbb R)$ with assigned boundary monodromy and nonzero Euler number, Pure Appl. Math. Q., 12 (2016), 399-462.
doi: 10.4310/PAMQ.2016.v12.n3.a3.
|
| [24] |
F. Palesi, Dynamics of the modular group action and Markov triples, Actes de Séminaire de Théorie Spectrale et Géométrie, 31 (2014), 137-161.
doi: 10.5802/tsg.298.
|
| [25] |
D. Pickrell and E. Z. Xia, Ergodicity of mapping class group actions on representation varieties. Ⅰ: Closed surfaces, Comment. Math. Helv., 77 (2002), 339-362.
doi: 10.1007/s00014-002-8343-1.
|
| [26] |
D. Pickrell and E. Z. Xia, Ergodicity of mapping class group actions on representation varieties. Ⅱ: Surfaces with boundary, Transform. Groups, 8 (2003), 397-402.
doi: 10.1007/s00031-003-0819-6.
|
| [27] |
J. P. Previte and E. Z. Xia, Topological dynamics on moduli spaces. Ⅰ, Pacific J. Math., 193 (2000), 397-417.
doi: 10.2140/pjm.2000.193.397.
|
| [28] |
J. P. Previte and E. Z. Xia, Topological dynamics on moduli spaces. Ⅱ, Trans. Amer. Math. Soc., 354 (2002), 2475-2494.
doi: 10.2140/pjm.2000.193.397.
|
| [29] |
J. P. Previte and E. Z. Xia, Dynamics of the mapping class group on the moduli of a punctured sphere with rational holonomy, Geom. Dedicata, 112 (2005), 65-72.
doi: 10.1007/s10711-004-5106-8.
|
| [30] |
C. Procesi, The invariant theory of $(n\times n)$ matrices, Adv. Math., 19 (1976), 306-381.
doi: 10.1016/0001-8708(76)90027-X.
|
Left: a
The standard pants decomposition of
Example of a triangle chain in the case
Visualisation of the action-angle
The curves
In black: the
A DT component isomorphic to a sphere and the locus
The curves
In black: the
The
The sub-sphere
The
The sub-spheres
The
A