We introduce a notion of stability for sheaves with respect to several polarisations
that generalises the usual notion of Gieseker stability. Under a boundedness
assumption which we show to hold on threefolds or for rank two sheaves on base
manifolds of arbitrary dimension, we prove that semistable sheaves have a projective
coarse moduli space that depends on a natural stability parameter. We then give two
applications of this machinery. First, we show that given a real ample class
on a smooth
projective threefold
there exists a projective moduli space of sheaves that are Gieseker semistable with respect
to
.
Second, we prove that given any two ample line bundles on
the
corresponding Gieseker moduli spaces are related by Thaddeus flips.
Keywords
Gieseker stability, variation of moduli spaces, chamber
structures, boundedness, moduli of quiver representations,
semistable sheaves on Kähler manifolds
Department of Pure Mathematics and
Mathematical Statistics
Centre for Mathematical Sciences
University of Cambridge
Wilberforce Road
Cambridge CB3 0WB
UK