88 research outputs found
Singular semipositive metrics in non-Archimedean geometry
Let X be a smooth projective Berkovich space over a complete discrete
valuation field K of residue characteristic zero, endowed with an ample line
bundle L. We introduce a general notion of (possibly singular) semipositive (or
plurisubharmonic) metrics on L, and prove the analogue of the following two
basic results in the complex case: the set of semipositive metrics is compact
modulo constants, and each semipositive metric is a decreasing limit of smooth
semipositive ones. In particular, for continuous metrics our definition agrees
with the one by S.-W. Zhang. The proofs use multiplier ideals and the
construction of suitable models of X over the valuation ring of K, using
toroidal techniques.Comment: 49 pages, 1 figure. Accepted in the Journal of Algebraic Geometr
Degree growth of meromorphic surface maps
We study the degree growth of iterates of meromorphic selfmaps of compact
Kahler surfaces. Using cohomology classes on the Riemann-Zariski space we show
that the degrees grow similarly to those of mappings that are algebraically
stable on some birational model.Comment: 17 pages, final version, to appear in Duke Math Journa
Uniruledness of stable base loci of adjoint linear systems with and without Mori Theory
We explain how to deduce from recent results in the Minimal Model Program a
general uniruledness theorem for base loci of adjoint divisors. We also show
how to recover special cases by extending a technique introduced by Takayama.Comment: version 2 : improved exposition ; relaxed hypotheses on singularitie
Equidistribution of Fekete points on complex manifolds
We prove the several variable version of the classical equidistribution
theorem for Fekete points of a compact subset of the complex plane, which
settles a well-known conjecture in pluri-potential theory. The result is
obtained as a special case of a general equidistribution theorem for Fekete
points in the setting of a given holomorphic line bundle over a compact complex
manifold. The proof builds on our recent work "Capacities and weighted volumes
for line bundles".Comment: 6 page
On the cohomology of pseudoeffective line bundles
The goal of this survey is to present various results concerning the
cohomology of pseudoeffective line bundles on compact K{\"a}hler manifolds, and
related properties of their multiplier ideal sheaves. In case the curvature is
strictly positive, the prototype is the well known Nadel vanishing theorem,
which is itself a generalized analytic version of the fundamental
Kawamata-Viehweg vanishing theorem of algebraic geometry. We are interested
here in the case where the curvature is merely semipositive in the sense of
currents, and the base manifold is not necessarily projective. In this
situation, one can still obtain interesting information on cohomology, e.g. a
Hard Lefschetz theorem with pseudoeffective coefficients, in the form of a
surjectivity statement for the Lefschetz map. More recently, Junyan Cao, in his
PhD thesis defended in Grenoble, obtained a general K{\"a}hler vanishing
theorem that depends on the concept of numerical dimension of a given
pseudoeffective line bundle. The proof of these results depends in a crucial
way on a general approximation result for closed (1,1)-currents, based on the
use of Bergman kernels, and the related intersection theory of currents.
Another important ingredient is the recent proof by Guan and Zhou of the strong
openness conjecture. As an application, we discuss a structure theorem for
compact K{\"a}hler threefolds without nontrivial subvarieties, following a
joint work with F.Campana and M.Verbitsky. We hope that these notes will serve
as a useful guide to the more detailed and more technical papers in the
literature; in some cases, we provide here substantially simplified proofs and
unifying viewpoints.Comment: 39 pages. This survey is a written account of a lecture given at the
Abel Symposium, Trondheim, July 201
Normal subgroups in the Cremona group (long version)
Let k be an algebraically closed field. We show that the Cremona group of all
birational transformations of the projective plane P^2 over k is not a simple
group. The strategy makes use of hyperbolic geometry, geometric group theory,
and algebraic geometry to produce elements in the Cremona group that generate
non trivial normal subgroups.Comment: With an appendix by Yves de Cornulier. Numerous but minors
corrections were made, regarding proofs, references and terminology. This
long version contains detailled proofs of several technical lemmas about
hyperbolic space
Green Currents for Meromorphic Maps of Compact K\"ahler Manifolds
We consider the dynamics of meromorphic maps of compact K\"ahler manifolds.
In this work, our goal is to locate the non-nef locus of invariant classes and
provide necessary and sufficient conditions for existence of Green currents in
codimension one.Comment: Statement of Theorem 1.5 is slightly improved. Proposition 5.2 and
Theorem 5.3 are adde
Positivity of relative canonical bundles and applications
Given a family of canonically polarized manifolds, the
unique K\"ahler-Einstein metrics on the fibers induce a hermitian metric on the
relative canonical bundle . We use a global elliptic
equation to show that this metric is strictly positive on , unless
the family is infinitesimally trivial.
For degenerating families we show that the curvature form on the total space
can be extended as a (semi-)positive closed current. By fiber integration it
follows that the generalized Weil-Petersson form on the base possesses an
extension as a positive current. We prove an extension theorem for hermitian
line bundles, whose curvature forms have this property. This theorem can be
applied to a determinant line bundle associated to the relative canonical
bundle on the total space. As an application the quasi-projectivity of the
moduli space of canonically polarized varieties
follows.
The direct images , , carry natural hermitian metrics. We prove an
explicit formula for the curvature tensor of these direct images. We apply it
to the morphisms that are induced by the Kodaira-Spencer map and obtain a differential
geometric proof for hyperbolicity properties of .Comment: Supercedes arXiv:0808.3259v4 and arXiv:1002.4858v2. To appear in
Invent. mat
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