On the second adjunction mapping. The case of a 1-dimensional image

Author:

Beltrametti Mauro,Sommese Andrew

Abstract

Let L ^ \widehat {L} be a very ample line bundle on an n n -dimensional projective manifold X ^ \widehat {X} , i.e., assume that L ^ i O P N ( 1 ) \widehat {L}\approx i^*\mathcal {O}_{\mathbb {P}_ N}(1) for some embedding i : X ^ P N i:\widehat {X}\hookrightarrow \mathbb {P}_ N . In this article, a study is made of the meromorphic map, φ ^ : X ^ Σ \widehat {\varphi } : \widehat {X}\to \Sigma , associated to | K X ^ + ( n 2 ) L ^ | |K_{\widehat {X}}+(n-2)\widehat {L}| in the case when the Kodaira dimension of K X ^ + ( n 2 ) L ^ K_{\widehat {X}}+(n-2)\widehat {L} is 3 \ge 3 , and φ ^ \widehat {\varphi } has a 1 1 -dimensional image. Assume for simplicity that n = 3 n=3 . The first main result of the paper shows that φ ^ \widehat \varphi is a morphism if either h 0 ( K X ^ + L ^ ) 7 h^0(K_{\widehat X}+\widehat L)\geq 7 or κ ( X ^ ) 0 \kappa (\widehat {X})\geq 0 . The second main result of this paper shows that if κ ( X ^ ) 0 \kappa (\widehat X)\ge 0 , then the genus, g ( f ) g(f) , of a fiber, f f , of the map induced by φ ^ \widehat \varphi on hyperplane sections is 6 \leq 6 . Moreover, if h 0 ( K X ^ + L ^ ) 21 h^0(K_{\widehat X}+\widehat L)\ge 21 then g ( f ) 5 g(f)\leq 5 , a connected component F F of a general fiber of φ ^ \widehat \varphi is either a K 3 K3 surface or the blowing up at one point of a K 3 K3 surface, and h 1 ( O X ^ ) 1 h^1(\mathcal {O}_{\widehat X})\le 1 . Finally the structure of the finite to one part of the Remmert-Stein factorization of φ ^ \widehat \varphi is worked out.

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

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