Generalised G2-structures and type IIB superstrings

The recent mathematical literature introduces generalised geometries which are defined by a reduction from the structure group SO(d,d) of the vector bundle Td+Td* to a special subgroup. In this article we show that compactification of IIB superstring vacua on 7-manifolds with two covariantly constant spinors leads to a generalised G2-structure associated with a reduction from SO(7,7) to G2xG2. We also consider compactifications on 6-manifolds where analogously we obtain a generalised SU(3)-structure associated with SU(3)xSU(3), and show how these relate to generalised G2-structures. (author)