Session 2. Algebraic Geometry

Twisted cubics on cubic fourfolds

Manfred Lehn, Johannes Gutenberg--Universität, Mainz, Germany
This is a report on joint work with C. Lehn, C. Sorger, D. van Straten, and with N. Addington
The moduli space of generalised twisted cubic curves on a smooth cubic fourfold Y that does not contain a plane is shown to be smooth, 10-dimensional and projective, and to admit a contraction to an 8-dimensional smooth variety \(Z(Y)\) that is irreducible holomorphic symplectic. Varying \(Z(Y)\) with \(Y\) gives a complete 20-dimensional family of projective holomorphic symplectic manifolds. If \(Y\) is a pfaffian cubic, \(Z(Y)\) is birational to the fourth Hilbert scheme of points on the K3-surface associated to Y by Beauville--Donagi.
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