( ~ North-Holland Publishing Company N = 8 SUPERGRAVITY

The complete structure of N = 8 supergravity is presented with an optional ocal SO(8) invariance. The SO(8) gauge interactions break E7 invariance, but leave the local SU(8) unaffected. Exploiting E 7 × SU(8) invariance and using explicit lowest order esults, we first derive the complete action and transformation laws. Subsequently, we introduce local SO(8) invariance and prove the consistency ofthe theory. Possible implications of our results are discussed. 1. In t roduct ion Already some years ago, supergravity was introduced in an attempt o fuse gravity with matter interactions in a consistent fashion [1] (for a general review of the subject, see ref. [2]). The largest extended supergravity theory is based on one irreducible multiplet of N = 8 supersymmetry, in which the graviton is naturally combined with particles of lower spin. This multiplet is unique in the sense that it is the only N = 8 supermultiplet containing maximal spin 2. Hence, the introduction of "matter " multiplets of low spin fields is not possible in this framework. This is just one aspect of the restrictive power of supergravity which makes it such an outstanding candidate for a unified description of elementary particles and thei