An explicit KO‐degree map and applications. Issue 1 (16th February 2017)

• Record Type: Journal Article
• Authors: Asok, Aravind; Fasel, Jean
• Is Part Of: Journal of topology. Volume 10:Issue 1(2017)
• Page Start: 268
• Page End: 300
• Publication Date: 2017-02-16
• Subjects: 14F42 -- 18F25 -- 19G38 -- 55R45 (primary); Topology -- Periodicals; 514.05
• DOI: 10.1112/topo.12007
• Languages: English
• ISSNs: 1753-8416

Abstract

Abstract: The goal of this note is to study the analog in unstable A 1 ‐homotopy theory of the unit map from the motivic sphere spectrum to the Hermitian K‐theory spectrum, that is, the degree map in Hermitian K‐theory. We show that 'Suslin matrices', which are explicit maps from odd‐dimensional split smooth affine quadrics to geometric models of the spaces appearing in Bott periodicity in Hermitian K‐theory, stabilize in a suitable sense to the unit map. As applications, we deduce that K i M W ( F ) = G W i i ( F ) for i ⩽ 3, which can be thought of as an extension of Matsumoto's celebrated theorem describing K 2 of a field. These results provide the first step in a program aimed at computing the sheaf π n A 1 ( A n ∖ 0 ) for n ⩾ 4 .