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Adjoint Linear Systems

Published online by Cambridge University Press:  27 June 2025

Herbert Clemens
Affiliation:
University of Utah
Janos Kollár
Affiliation:
University of Utah
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Summary

This note describes some of the recent methods and effective results in the study of pluricanonical and adjoint linear systems on higherdimensional varieties. We describe an algebraic construction for the multiplier ideals and we use it to give a simple proof for the Reider theorem.

§1. The purpose of this note is to survey some of the recent results on pluricanonical and adjoint linear systems on algebraic varieties. Let A be a nef and big divisor on a smooth projective variety X. We would like to study the linear system |Kx + A|. For X a curve, it is well known that if deg A ≥ 2, the linear system |Kx + A| is free, and if deg A ≥ 3, then Kx + A is very ample. The canonical linear system |Kx| is very ample if and only if X is not a hyperelliptic curve. From the theory of curves, we know that the properties of these linear systems are closely related to the geometry of the curve. It is natural that one would like to obtain similar numerical criteria for freeness and very ampleness for adjoint linear systems on a higher-dimensional variety, and study their geometric properties.

Many results and ideas in this note are based on my joint work with R. Lazarsfeld. I would like to thank him for sharing with me many of his ideas. For surfaces of general type, Kodaira [Kod], Bombieri [Bmb] and many others have studied the behavior of the pluricanonical maps.

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Publisher: Cambridge University Press
Print publication year: 1996

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