Published online by Cambridge University Press: 01 May 2009
Let X be a smooth projective curve of genus g ≥ 2 over ℂ. A pair (E, φ) over X consists of an algebraic vector bundle E over X and a section φ ∈ H0(E). There is a concept of stability for pairs which depends on a real parameter τ. Here we prove that the third cohomology groups of the moduli spaces of τ-stable pairs with fixed determinant and rank n ≥ 2 are polarised pure Hodge structures, and they are isomorphic to H1(X) with its natural polarisation (except in very few exceptional cases). This implies a Torelli theorem for such moduli spaces. We recover that the third cohomology group of the moduli space of stable bundles of rank n ≥ 2 and fixed determinant is a polarised pure Hodge structure, which is isomorphic to H1(X). We also prove Torelli theorems for the corresponding moduli spaces of pairs and bundles with non-fixed determinant.