N=8 gaugings revisited: an exhaustive classification

In this paper we reconsider, for N = 8 supergravity, the problem of gauging the most general electric subgroup. We show that admissible theories are fully characterized by a single algebraic equation to be satisfied by the embedding G(gauge) --> SL(8,R) subset of E-7(7) The complete set of solutions to this equation contains 36 parameters. Modding by the action of SL(8, R)) conjugations that yield equivalent theories all continuous parameters are eliminated except for an overall coupling constant and we obtain a discrete set of orbits. This set is in one-to-one correspondence with 36 Lie subalgebras of SL(8,R), corresponding to all possible real forms of the SO(8) Lie algebra plus a set of contractions thereof. By means of our analysis we establish the theorem that the N = 8 gaugings constructed by Hurl in the middle eighties constitute the exhaustive set of models. As a corollary we show that there exists a unique seven-dimensional abelian gauging. The corresponding abelian algebra is not contained in the maximal abelian ideal of the salvable Lie algebra generating the scalar manifold E-7(7)/SU(8) (C) 1998 Elsevier Science B.V.