“…As in Laszlo [14] (see also Narasimhan-Ramanan [17] and Pauly [21]), we can find an étale affine neighbourhood S = Spec(A) of E in U and a family of stable vector bundles E over S × X such that for each F ∈ S, we have E| {F }×X ∼ = F , together with a homomorphism μ: M → N of flat A-modules of finite type such that for all A-modules P , by functoriality,…”
Let E and F be vector bundles over a complex projective smooth curve X, and suppose that 0 → E → W → F → 0 is a nontrivial extension. Let G ⊆ F be a subbundle and D an effective divisor on X. We give a criterion for the subsheaf G(−D) ⊂ F to lift to W , in terms of the geometry of a scroll in the extension space PH 1 (X, Hom(F, E)). We use this criterion to describe the tangent cone to the generalised theta divisor on the moduli space of semistable bundles of rank r and slope g − 1 over X, at a stable point. This gives a generalisation of a case of the Riemann-Kempf singularity theorem for line bundles over X. In the same vein, we generalise the geometric Riemann-Roch theorem to vector bundles of slope g − 1 and arbitrary rank.
“…As in Laszlo [14] (see also Narasimhan-Ramanan [17] and Pauly [21]), we can find an étale affine neighbourhood S = Spec(A) of E in U and a family of stable vector bundles E over S × X such that for each F ∈ S, we have E| {F }×X ∼ = F , together with a homomorphism μ: M → N of flat A-modules of finite type such that for all A-modules P , by functoriality,…”
Let E and F be vector bundles over a complex projective smooth curve X, and suppose that 0 → E → W → F → 0 is a nontrivial extension. Let G ⊆ F be a subbundle and D an effective divisor on X. We give a criterion for the subsheaf G(−D) ⊂ F to lift to W , in terms of the geometry of a scroll in the extension space PH 1 (X, Hom(F, E)). We use this criterion to describe the tangent cone to the generalised theta divisor on the moduli space of semistable bundles of rank r and slope g − 1 over X, at a stable point. This gives a generalisation of a case of the Riemann-Kempf singularity theorem for line bundles over X. In the same vein, we generalise the geometric Riemann-Roch theorem to vector bundles of slope g − 1 and arbitrary rank.
“…It is stated in [3] that it can be easily deduced from the results of that paper that the map X → M 0 is also injective. This would imply that the curve X can be identified with M 0 .…”
Section: Introductionmentioning
confidence: 90%
“…The bundles U x were shown to be semistable in [1, Proposition 2.4], but the proof does not seem to imply stability directly, even though we know also by [3] that U x is simple.…”
Abstract. Let M denote the moduli space of stable vector bundles of rank n and fixed determinant of degree coprime to n on a non-singular projective curve X of genus g ≥ 2. Denote by U a universal bundle on X × M . We show that, for x, y ∈ X, x = y, the restrictions U|{x} × M and U|{y} × M are stable and nonisomorphic when considered as bundles on X.
Abstract. We study the ring generated by the Chern classes of tautological line bundles on the moduli space of parabolic bundles of arbitrary rank on a Riemann surface. We show the Poincaré duals to these Chern classes have simple geometric representatives. We use this construction to show that the ring generated by these Chern classes vanishes below the dimension of the moduli space, in analogy with the Newstead-Ramanan conjecture for stable bundles.
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