Reflections

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Unformatted text preview: BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 45, Number 1, January 2008, Pages 1–60 S 0273-0979(07)01190-1 Article electronically published on October 26, 2007 REFLECTION GROUPS IN ALGEBRAIC GEOMETRY IGOR V. DOLGACHEV To Ernest Borisovich Vinberg Abstract. After a brief exposition of the theory of discrete reflection groups in spherical, euclidean and hyperbolic geometry as well as their analogs in complex spaces, we present a survey of appearances of these groups in various areas of algebraic geometry. 1. Introduction The notion of a reflection in a euclidean space is one of the fundamental notions of symmetry of geometric figures and does not need an introduction. The theory of discrete groups of motions generated by reflections originates in the study of plane regular polygons and space polyhedra, which goes back to ancient mathematics. Nowadays it is hard to find a mathematician who has not encountered reflection groups in his area of research. Thus a geometer sees them as examples of discrete groups of isometries of Riemannian spaces of constant curvature or examples of special convex polytopes. An algebraist finds them in group theory, especially in the theory of Coxeter groups, invariant theory and representation theory. A combinatorialist may see them in the theory of arrangements of hyperplanes and combinatorics of permutation groups. A number theorist meets them in arithmetic theory of quadratic forms and modular forms. For a topologist they turn up in the study of hyperbolic real and complex manifolds, low-dimensional topology and singularity theory. An analyst sees them in the theory of hypergeometric functions and automorphic forms, complex higher-dimensional dynamics and ordinary differential equations. All of the above and much more appears in algebraic geometry. The goal of this survey is to explain some of “much more”. One finds an extensive account of the history of the theory of reflection groups in euclidean and spherical spaces in Bourbaki’s Groupes et Alg`bres de Lie, Chapters e IV-VI. According to this account the modern theory originates from the works of geometers A. M¨bius and L. Schl¨fli in the middle of the 19th century, then was o a extended and applied to the theory of Lie algebras in the works of E. Cartan and W. Killing at the end of the same century, and culminated in the works of H. S. M. Coxeter [27]. The first examples of reflection groups in hyperbolic plane go back to F. Klein and H. Poincar´ at the end of the 19th century. e Received by the editors December 3, 2006, and, in revised form, May 17, 2007. 2000 Mathematics Subject Classification. Primary 20F55, 51F15, 14E02; Secondary 14J28, 14E07, 14H20, 11H55. The author was supported in part by NSF grant no. 0245203. c 2007 American Mathematical Society 1 2 IGOR V. DOLGACHEV It is not general knowledge that reflection groups, finite and infinite, appeared in 1885-1895 in the works of S. Kantor [63] on classification of subgroups of the Cremona group of...
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This note was uploaded on 02/24/2012 for the course MATH 285 taught by Professor Igordolgachev during the Fall '04 term at University of Michigan-Dearborn.

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