# Martin Gulbrandsen: Geometry of wall crossings for the Hilbert scheme of skew lines

**Time: **
Tue 2021-10-26 14.30 - 15.30

**Location: **
Institut Mittag-Leffler, Seminar Hall Kuskvillan (alt. Zoom, meeting ID: 921 756 1880)

**Participating: **
Martin Gulbrandsen (University of Stavanger)

**Abstract:** The Hilbert scheme of space curves with Hilbert polynomial \(2t+2\) has two components, parametrizing pairs of skew lines on the one hand, and conics union a point on the other. B. Schmidt has developed a technique for analysing Bridgeland wall crossings on threefolds, and applied this to twisted cubics and their deformations. Our example with skew lines and their deformations has similar behaviour, and Schmidt's machinery may be applied and yields two wall crossings corresponding to a contraction of each of the two Hilbert scheme components. In this talk I seek to understand the two wall crossing conractions in terms of Mori theory, and find that each is a contraction of a *K*-negative extremal ray. In particular, all moduli spaces appearing are projective varieties.