An additive variant of the differential symbol maps

Our investigation focuses on an additive analogue of the Bloch-Gabber-Kato theorem which establishes a relation between the Milnor K-group of a field of positive characteristic and a Galois cohomology group of the field. Extending the Aritin-Schreier-Witt theory, we present an isomorphism from the Mackey product associated with the Witt group and the multiplicative groups to a Galois cohomology group. As a result, we give an expression for the torsion subgroup of the Brauer group of a field.