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Action of the mapping class group on character varieties and Higgs bundles

We consider the action of a finite subgroup of the mapping class group $Mod(S)$ of an oriented compact surface $S$ of genus $g \geq 2$ on the moduli space $\mathcal{R}(S,G)$ of representations of $π_1(S)$ in a connected semisimple real Lie group $G$. Kerckhoff's solution of the Nielsen realization problem ensures the existence of an element $J$ in the Teichmüller space of $S$ for which $Γ$ can be realised as a subgroup of the group of automorphisms of $X=(S,J)$ which are holomorphic or antiholomorphic. We identify the fixed points of the action of $Γ$ on $\mathcal{R}(S,G)$ in terms of $G$-Higgs bundles on $X$ equipped with a certain twisted $Γ$-equivariant structure, where the twisting involves abelian and non-abelian group cohomology simultaneously. When the kernel of the isotropy representation of the maximal compact subgroup of $G$ is trivial, the fixed points can be described in terms of familiar objects on $Y=X/Γ^+$, where $Γ^+ \subset Γ$ is the maximal subgroup of $Γ$ consisting of holomorphic automorphisms of $X$. If $Γ=Γ^+$ one obtains actual $Γ$-equivariant $G$-Higgs bundles on $X$, which in turn correspond with parabolic Higgs bundles on $Y=X/Γ$ (this generalizes work of Nasatyr \& Steer for $G=SL(2,\mathbb{R})$ and Boden, Andersen & Grove and Furuta & Steer for $G=SU(n)$). If on the other hand $Γ$ has antiholomorphic automorphisms, the objects on $Y=X/Γ^+$ correspond with pseudoreal parabolic Higgs bundles. This is a generalization in the parabolic setup of the pseudoreal Higgs bundles studied by the first author in collaboration with Biswas & Hurtubise.