On symplectic aspects of SU(2) character varieties for punctured surfaces
Abstract
For a surface with an odd number of punctures, the moduli space of flat SU(2) connections with traceless holonomy around each puncture is a symplectic manifold. When the moduli space is nonempty, there is a natural homomorphism from the mapping class group of the punctured surface to the symplectic mapping class group of this moduli space. It is shown that this homomorphism is injective if and only if the dimension of the moduli space is greater than $2$. This generalizes work of Seidel and Wehrheim--Woodward. Also given is a complete classification of Lagrangian spheres in the projective plane blown up at $5$ points with its monotone symplectic structure, which is the moduli space for the 5-punctured sphere. Furthermore, it is determined when two such Lagrangian spheres can be displaced by a symplectic isotopy. Results are also obtained regarding Lagrangian spheres in the intersection of two quadrics in ℂℙ5. The proofs involve instanton Floer theory and results on Heegaard splittings. A main technical result establishes the approximation of any Hamiltonian isotopy of the SU(2) moduli space by holonomy perturbations which are used in instanton homology.
Related
- Compactification of SL(3,ℂ)-Character Varieties of Surfaces via Skein Algebras
- Character variety of the five-punctured sphere and the determinantal quintic hypersurface
- Deep Points of Cluster Algebras II: Punctured Marked Surfaces
- On symplectic aspects of μ-equivalence of a class of isolated hypersurface singularities
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BibTeX
@misc{daemi2026symplectic,
title = {{On symplectic aspects of $SU(2)$ character varieties for punctured surfaces}},
author = {Aliakbar Daemi and Christopher Scaduto},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28907},
eprint = {2609.28907},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28907},
}
RIS
TY - UNPB
TI - On symplectic aspects of SU(2) character varieties for punctured surfaces
AU - Aliakbar Daemi
AU - Christopher Scaduto
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.28907
UR - https://arxiv.org/abs/2609.28907
AB - For a surface with an odd number of punctures, the moduli space of flat SU(2) connections with traceless holonomy around each puncture is a symplectic manifold. When the moduli space is nonempty, there is a natural homomorphism from the mapping class group of the punctured surface to the symplectic mapping class group of this moduli space. It is shown that this homomorphism is injective if and only if the dimension of the moduli space is greater than $2$. This generalizes work of Seidel and Wehrheim--Woodward. Also given is a complete classification of Lagrangian spheres in the projective plane blown up at $5$ points with its monotone symplectic structure, which is the moduli space for the 5-punctured sphere. Furthermore, it is determined when two such Lagrangian spheres can be displaced by a symplectic isotopy. Results are also obtained regarding Lagrangian spheres in the intersection of two quadrics in ℂℙ^5. The proofs involve instanton Floer theory and results on Heegaard splittings. A main technical result establishes the approximation of any Hamiltonian isotopy of the SU(2) moduli space by holonomy perturbations which are used in instanton homology.
ER -