Witt Groups of Curves and Surfaces

TL;DR

This paper investigates the structure of Witt groups for smooth curves and surfaces over algebraically closed fields, providing explicit calculations and exploring their connections with topological K-theory.

Contribution

It offers a complete determination of classical and shifted Witt groups for curves and surfaces, including a detailed description of Grothendieck-Witt groups and their relation to topological K-groups.

Findings

Witt groups of curves and surfaces are explicitly computed.

Witt groups relate closely to real topological K-groups for certain surfaces.

The results unify algebraic and topological perspectives on these varieties.

Abstract

We study Witt groups of smooth curves and surfaces over algebraically closed fields of characteristic not two. In both dimensions, we determine both the classical Witt group and Balmer's shifted Witt groups. In the case of curves, the results are supplemented with a complete description of the (shifted) Grothendieck-Witt groups. In a second step, we analyse the relationship of Witt groups of smooth complex curves and surfaces with their real topological K-groups. They turn out to be surprisingly close: for all curves and for all projective surfaces of geometric genus zero, the Witt groups may be identified with the quotients of their even KO-groups by the images of their complex topological K-groups under realification.