Let A be a regular local ring containing 1/2, which is either equicharacteristic, or is smooth over a d.v.r. of mixed characteristic. We prove that the product maps on derived Grothendieck-Witt groups of A satisfy the following property: given two elements with supports which do not intersect properly, their product vanishes. This gives an analogue for “oriented intersection multiplicites” of S...

We give explicit descriptions of the Witt vectors of the Boolean semiring. This includes the big Witt vectors, the Schur Witt vectors, and the p-typical Witt vectors. We use this to determine the Schur Witt vectors of the natural numbers, which can be viewed as the classification of totally positive power series with integral coefficients, first observed by Davydov. We also determine the cardin...

s for Plenary Speakers André Joyal, Université du Québec à Montréal “The Witt vectors construction revisited” Abstract: Witt vectors are playing an important role in number theory and topology. Introduced by Witt in 1937, they were generalised by Cartier in 1967. But they remain mysterious objects with surprisingly many facets. We shall describe the Witt vector construction as a right adjoint t...

This is an account of the algebraic geometry of Witt vectors and arithmetic jet spaces. The usual, “p-typical” Witt vectors of p-adic schemes of finite type are already reasonably well understood. The main point here is to generalize this theory in two ways. We allow not just p-typical Witt vectors but those taken with respect to any set of primes in any ring of integers in any global field, fo...

To a short exact sequence of triangulated categories with duality, we associate a long exact sequence of Witt groups. For this, we introduce higher Witt groups in a very algebraic and explicit way. Since those Witt groups are 4-periodic, this long exact sequence reduces to a cyclic 12-term one. Of course, in addition to higher Witt groups, we need to construct connecting homomorphisms, hereafte...

This note provides a computation of the bordism groups of K-Witt spaces for fields K with characteristic 2. We provide a complete computation for the unoriented bordism groups. For the oriented bordism groups, a nearly complete computation is provided as well a discussion of the difficulty of resolving a remaining ambiguity in dimensions equivalent to 2 mod 4. This corrects an error in the char...