Goldman form, flat connections and stable vector bundles

Abstract

We consider the moduli space $\mathcal{N}$ of stable vector bundles of degree $0$ over a compact Riemann surface and the affine bundle $\mathcal{A}\to \mathcal{N}$ of flat connections. Following the similarity between the Teichmüller spaces and the moduli of bundles, we introduce the analogue of of the quasi-Fuchsian projective connections - local holomorphic sections of $\mathcal{A}$ - that allow to pull back the Liouville symplectic form on $T^{\ast }\mathcal{N}$ to $\mathcal{A}$. We prove that the pullback of the Goldman form to $\mathcal{A}$ by the Riemann-Hilbert correspondence coincides with the pullback of the Liouville form. We also include a simple proof, in the spirit of Riemann bilinear relations, of the classic result - the pullback of Goldman symplectic form to $\mathcal{N}$ by the Narasimhan-Seshadri connection is the natural symplectic form on $\mathcal{N}$, introduced by Narasimhan and Atiyah & Bott.

Final version, typos corrected and exposition improved. To appear in L'Enseignement Mathematique