On geometrical structure of compactified subspaces in d=11 supergravity

It is shown that all known vacuum configurations of the d=11 supergravity and a number of new configurations arising as a result of Freund-Rubin spontaneous compactification have a structure of the bundled space P(N6, S1) with Kaluza-Klein standard metric. The most interesting of the found vacuum states conserve N=3.1 supersymmetries in the effective 4-dimensional theory and are invariant under transformations of the supergroups OSp(4.3)xSU(3) and OSp(4.1)xSU(3)xSU(2), respective-ly. New N=2 supersymmetric vacuum configurations are found characterized by the symmetry groups OSp(4.2)xSO(5) and OSp(4.2)xSU(2)xSU(2)xSU(2)