Cohomological invariants of quaternionic skew-hermitian forms

Abstract.

We define a complete system of invariants e _n,Q ,n ≥ 0 for quaternionic skew-hermitian forms, which are twisted versions of the invariants e _n for quadratic forms. We also show that quaternionic skew-hermitian forms defined over a field of 2-cohomological dimension at most 3 are classified by rank, discriminant, Clifford invariant and Rost invariant.