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April 11, 2014
Friday, April 11
Algebra Seminar
Time: 15:00
Speaker: Kirsten Wickelgren (Georgia Tech)
Title: "Splitting varieties for triple Massey products in Galois cohomology"
Room: MC 107

Abstract: The Brauer-Severi variety a x2+by2=z2 has a rational point if and only if the cup product of cohomology classes with F2 coefficients associated to a and b vanish. The cup product is the order-2 Massey product. Higher Massey products give further structure to Galois cohomology, and more generally, they measure information carried in a differential graded algebra which can be lost on passing to the associated cohomology ring. For example, the cohomology of the Borromean rings is isomorphic to that of three unlinked circles, but non-trivial Massey products of elements of H1 detect the more complicated structure of the Borromean rings. Analogues of this example exist in Galois cohomology due to work of Morishita, Vogel, and others. This talk will first introduce Massey products and some relationships with non-abelian cohomology. We will then show that bx2= (y21ay22 +cy23acy24)2c(2y1y32ay2y4)2 is a splitting variety for the triple Massey product a,b,c with F2 coefficients, and that this variety satisfies the Hasse principle. It follows that all triple Massey products over global fields vanish when they are defined. Jan Minac and Nguyen Duy Tan have extended this result to all Fp and with p=2 to all fields of characteristic different from 2. The method discussed in the talk could produce splitting varieties for higher order Massey products. This is joint work with Michael Hopkins.