DIMENSIONAL REDUCTION OF TYPE-IIB SUPERGRAVITY AND EXCEPTIONAL QUATERNIONIC MANIFOLDS

The authors describe the SU(3) invariant reduction of the type IIB supergravity from ten to four dimensions, and show that the low-energy scalars parametrise the quaternionic sigma model G2,2/SO(4). They identify the scalar Lagrangian with the one obtained from a similar SU(3) truncation of the type IIA theory, followed by a dimensional reduction to three dimensions. This is an explicit realisation of the c map, that in general relates the low-energy Lagrangians of the type-II superstrings when compactified on the same (2, 2) superconformal theory.