DELIGNE, PIERRE REN

born Oct. 3, 1944, Brussels, Belg. Belgian mathematician who was awarded the Fields Medal at the International Congress of Mathematicians in Helsinki, Fin., in 1978 for his work in algebraic geometry. Deligne received a bachelor's degree in mathematics (1966) and a doctorate (1968) from the Free University of Brussels. After a year at the National Foundation for Scientific Research, Brussels, he joined the Institute of Advanced Scientific Studies, Bures-sur-Yvette, France, in 1968. In 1984 he became a professor at the Institute for Advanced Study, Princeton, N.J., U.S. In 1949 the French mathematician Andr Weil made a series of conjectures concerning zeta functions of curves of abelian varieties. One of these was the equivalent of the Riemann hypothesis for varieties over finite fields. Deligne used a new theory of cohomology called talestable cohomology, drawing on ideas originally developed by Alexandre Grothendieck some 15 years earlier, and applied them with great success to the Weil conjectures. Deligne's work provided important insights into the relationship between algebraic geometry and algebraic number theory. He also developed an area of mathematics called weight theory, which has applications in the solution of differential equations. Later he proved some conjectures by the British topologist Sir William Vallance Douglas Hodge. Deligne's publications include quations diffrentielles points singuliers rguliers (1970; Differential Equations with Regular Singular Points); Groupes de monodromie en gomtrie algbrique (1973; Monodromy Groups in Algebraic Geometry); Modular Functions of One Variable (1973); with Jean-Francois Boutot et al., Cohomologie tale (1977; tale Cohomologies); and, with J. Milne, A. Ogus, and K. Shih, Hodge Cycles, Motives, and Shimura Varieties (1982).