Subtle Stiefel-Whitney classes

Alexander Vishik (University of Nottingham)

Monday 1st December, 2014 16:00-17:00 Maths 326


(This is a joint work with Alexander Smirnov.) I will discuss the new “subtle” version of Stiefel-Whitney classes of quadratic forms, which is much more informative than the classical one introduced by Delzant and Milnor. In particular, our classes see the powers of the fundamental ideal of the Witt ring, as well as the Arason invariant and it’s higher analogues, are also related to the J-invariant of quadrics, and are essential for the motivic description of some homogeneous varieties associated to a quadratic form. They serve as a building block in the new homotopic approach to the classification of torsors of an orthogonal group.  

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