On G/H geometry and its use in M-theory compactifications

The Riemannian geometry of coset spaces is reviewed, with emphasis on its applications to supergravity and M-theory compactifications. Formulae for the connection and curvature of rescaled coset manifolds are generalized to the case of nondiagonal Killing metrics. The example of the N^{010} spaces is discussed in detail. These are a subclass of the coset manifolds N^{pqr}=G/H = SU(3) x U(1)/U(1) x U(1), the integers p,q,r characterizing the embedding of H in G. We study the realization of N^{010} as G/H=SU(3) x SU(2)/U(1) x SU(2) (with diagonal embedding of the SU(2) \in H into G). For a particular G-symmetric rescaling there exist three Killing spinors, implying N=3 supersymmetry in the AdS_4 \times N^{010} compactification of D=11 supergravity. This rescaled N^{010} space is of particular interest for the AdS_4/CFT_3 correspondence, and its SU(3) x SU(2) isometric realization is essential for the OSp(4|3) classification of the Kaluza-Klein modes.