We study compactifications of type IIA supergravity on six-dimensional manifolds with SU(2) structure and compute the low-energy effective action in terms of the nontrivial intrinsic torsion. The consistency with gauged N = 4 supergravity is established and the gauge group is determined. Depending on the structure of the intrinsic torsion, antisymmetric tensor fields can become massive.

We investigate the effective theory of type IIA string theory on six-dimensional orientifold backgrounds with SU(2)-structure. We focus on the case of orientifolds with O6-planes, for which we compute the bosonic effective action in the supergravity approximation. For a generic SU(2)-structure background, we find that the low-energy effective theory is a gauged N = 2 supergravity where moduli in both vector and hypermultiplets are charged. Since all these supergravities descend from a corresponding N = 4 background, their scalar target space is always a quotient of a SU(1, 1)/U(1) × SO(6, n)/SO(6) × SO(n) coset, and is therefore also very constrained.