Author:
Bérczi Gergely,Kirwan Frances
Abstract
AbstractLet $H$
H
be a complex linear algebraic group with internally graded unipotent radical acting on a complex projective variety $X$
X
. Given an ample linearisation of the action and an associated Fubini–Study Kähler form which is invariant for a maximal compact subgroup $Q$
Q
of $H$
H
, we define a notion of moment map for the action of $H$
H
, and under suitable conditions (that the linearisation is well-adapted and semistability coincides with stability) we describe the (non-reductive) GIT quotient $X/\!/H$
X
/
/
H
introduced in (Bérczi et al. in J. Topol. 11(3):826–855, 2018) in terms of this moment map. Using this description we derive formulas for the Betti numbers of $X/\!/H$
X
/
/
H
and express the rational cohomology ring of $X/\!/H$
X
/
/
H
in terms of the rational cohomology ring of the GIT quotient $X/\!/T^{H}$
X
/
/
T
H
, where $T^{H}$
T
H
is a maximal torus in $H$
H
. We relate intersection pairings on $X/\!/H$
X
/
/
H
to intersection pairings on $X/\!/T^{H}$
X
/
/
T
H
, obtaining a residue formula for these pairings on $X/\!/H$
X
/
/
H
analogous to the residue formula of (Jeffrey and Kirwan in Topology 34(2):291–327, 1995). As an application, we announce a proof of the Green–Griffiths–Lang and Kobayashi conjectures for projective hypersurfaces with polynomial degree.
Funder
Royal Danish Library, Aarhus University Library
Publisher
Springer Science and Business Media LLC
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