Deformations of the generalised Picard bundle |
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Authors: | I Biswas |
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Institution: | a School of Mathematics, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India b CIMAT, Apdo. Postal 402, C.P. 36240, Guanajuato, Gto, México c Department of Mathematical Sciences, The University of Liverpool, Peach Street, Liverpool, L69 7ZL, England, UK |
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Abstract: | Let X be a nonsingular algebraic curve of genus g?3, and let Mξ denote the moduli space of stable vector bundles of rank n?2 and degree d with fixed determinant ξ over X such that n and d are coprime. We assume that if g=3 then n?4 and if g=4 then n?3, and suppose further that n0, d0 are integers such that n0?1 and nd0+n0d>nn0(2g-2). Let E be a semistable vector bundle over X of rank n0 and degree d0. The generalised Picard bundle Wξ(E) is by definition the vector bundle over Mξ defined by the direct image where Uξ is a universal vector bundle over X×Mξ. We obtain an inversion formula allowing us to recover E from Wξ(E) and show that the space of infinitesimal deformations of Wξ(E) is isomorphic to H1(X,End(E)). This construction gives a locally complete family of vector bundles over Mξ parametrised by the moduli space M(n0,d0) of stable bundles of rank n0 and degree d0 over X. If (n0,d0)=1 and Wξ(E) is stable for all E∈M(n0,d0), the construction determines an isomorphism from M(n0,d0) to a connected component M0 of a moduli space of stable sheaves over Mξ. This applies in particular when n0=1, in which case M0 is isomorphic to the Jacobian J of X as a polarised variety. The paper as a whole is a generalisation of results of Kempf and Mukai on Picard bundles over J, and is also related to a paper of Tyurin on the geometry of moduli of vector bundles. |
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Keywords: | 14H60 14J60 |
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