SIMPLE VECTOR BUNDLES on PLANE DEGENERATIONS of an ELLIPTIC CURVE 1. Introduction the Theory of Vector Bundles on an Elliptic Cu
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 364, Number 1, January 2012, Pages 137–174 S 0002-9947(2011)05354-7 Article electronically published on August 25, 2011 SIMPLE VECTOR BUNDLES ON PLANE DEGENERATIONS OF AN ELLIPTIC CURVE LESYA BODNARCHUK, YURIY DROZD, AND GERT-MARTIN GREUEL Abstract. In 1957 Atiyah classified simple and indecomposable vector bun- dles on an elliptic curve. In this article we generalize his classification by describing the simple vector bundles on all reduced plane cubic curves. Our main result states that a simple vector bundle on such a curve is completely determined by its rank, multidegree and determinant. Our approach, based on the representation theory of boxes, also yields an explicit description of the corresponding universal families of simple vector bundles. 1. Introduction The theory of vector bundles on an elliptic curve and its degenerations is known to be closely related with the theory of integrable systems (see e.g. [Kri77, Ma78, Mu94]). Another motivation for studying vector bundles on elliptic fibrations comes from the work of Friedman, Morgan and Witten [FMW99], who discovered their importance for heterotic string theory. The main motivation of our investigation was the following problem. Let E → T be an elliptic fibration, where T is some basis such that for any point t ∈ T the fiber Et is a reduced projective curve with the trivial dualizing sheaf. E t E E 0 E t • t • T t• 0 In most applications, a generic fiber of this fibration is an elliptic curve and for the points of the discriminant locus Δ ⊂ T the fibers are singular (and possibly reducible).
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