English

Contractions on a manifold polarized by an ample vector bundle

alg-geom 2015-06-30 v1 Algebraic Geometry

Abstract

A complex manifold XX of dimension nn together with an ample vector bundle EE on it will be called a {\sf generalized polarized variety}. The adjoint bundle of the pair (X,E)(X,E) is the line bundle KX+det(E)K_X + det(E). We study the positivity (the nefness or ampleness) of the adjoint bundle in the case r:=rank(E)=(n2)r := rank (E) = (n-2). If r(n1)r\geq (n-1) this was previously done in a series of paper by Ye-Zhang, Fujita, Andreatta-Ballico-Wisniewski. If KX+detEK_X+detE is nef, then by the Kawamata-Shokurov base point free theorem, it supports a contraction; i.e. a map π:XW\pi :X \longrightarrow W from XX onto a normal projective variety WW with connected fiber and such that KX+det(E)=πHK_X + det(E) = \pi^*H, for some ample line bundle HH on WW. We describe those contractions for which dimF(r1)dimF \leq (r-1). We extend this result to the case in which XX has log terminal singualarities. In particular this gives the Mukai's conjecture1 for singular varieties. We consider also the case in which dimF=rdimF = r for every fibers and π\pi is birational. Hard copies of the paper are available.

Keywords

Cite

@article{arxiv.alg-geom/9410029,
  title  = {Contractions on a manifold polarized by an ample vector bundle},
  author = {M. Andreatta and M. Mella},
  journal= {arXiv preprint arXiv:alg-geom/9410029},
  year   = {2015}
}

Comments

18 pages, LateX