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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2507.19191 |
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| _version_ | 1866914018263826432 |
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| author | Camacho-Cadena, Fernando |
| author_facet | Camacho-Cadena, Fernando |
| contents | The character variety $\mathscr{X}(S,G)$ associated to an oriented compact surface $S$ with boundary and a real reductive Lie group $G$ admits a Poisson structure and is foliated by symplectic leaves. When $G$ is a matrix group, any closed curve $c\inπ_1(S)$ induces a trace function $\mathsf{tr}_c\colon[ρ]\mapsto \mathsf{tr}(ρ(c))$ on $\mathscr{X}(S,G)$. In this article, we study the Hamiltonian flows of trace functions associated to self-intersecting curves. We prove that when $G=\mathsf{PSL}(3,\mathbb{R})$ and $S$ is the pair of pants, every orbit of the Hamiltonian flow of the trace of a figure eight curve on $S$ is periodic and has a unique fixed point. The proof uses explicit computations in Fock-Goncharov coordinates. As an application, we prove a similar statement for the trace of the $Θ$-web. Finally, we focus on the symplectic leaf corresponding to the unipotent locus, and derive similar results for two more self-intersecting curves: the commutator, and a curve going $k$ times around a boundary component. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_19191 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Self-intersecting curves on a pair of pants and periodic orbits of Hamiltonian flows Camacho-Cadena, Fernando Geometric Topology Differential Geometry The character variety $\mathscr{X}(S,G)$ associated to an oriented compact surface $S$ with boundary and a real reductive Lie group $G$ admits a Poisson structure and is foliated by symplectic leaves. When $G$ is a matrix group, any closed curve $c\inπ_1(S)$ induces a trace function $\mathsf{tr}_c\colon[ρ]\mapsto \mathsf{tr}(ρ(c))$ on $\mathscr{X}(S,G)$. In this article, we study the Hamiltonian flows of trace functions associated to self-intersecting curves. We prove that when $G=\mathsf{PSL}(3,\mathbb{R})$ and $S$ is the pair of pants, every orbit of the Hamiltonian flow of the trace of a figure eight curve on $S$ is periodic and has a unique fixed point. The proof uses explicit computations in Fock-Goncharov coordinates. As an application, we prove a similar statement for the trace of the $Θ$-web. Finally, we focus on the symplectic leaf corresponding to the unipotent locus, and derive similar results for two more self-intersecting curves: the commutator, and a curve going $k$ times around a boundary component. |
| title | Self-intersecting curves on a pair of pants and periodic orbits of Hamiltonian flows |
| topic | Geometric Topology Differential Geometry |
| url | https://arxiv.org/abs/2507.19191 |