Attempts at superunification

We describe attempts to construct a phenomenologically viable model which embeds a unified theory of strong, weak and electromagnetic interactions in an extended supergravity theory. Following Cremmer and Julia, we assume that the local unitary symmetry which they found for SO(N) supergravity theories is realized dynamically, and that the usual quarks, leptons, gauge bosons and Higgs scalars of the renormalizable gauge theory are composite states which appear point-like on a mass scale below the Planck mass. We argue that this picture leads uniquely to SO(8) (or SO(7)) supergravity with SU(5) as the grand unification gauge group. We find that conventional symmetry breaking schemes according to which particles acquire all allowed invariant masses at each stage of a step by step symmetry breakdown do not yield an acceptable particle spectrum. We argue that the original symmetries of the composite supermultiplet may break dynamically to an effective anomaly free renormalizable sub-theory, with the underlying supersymmetry serving at most to restrict the particle spectrum and to specify the couplings of the effective renormalizable Lagrangian at the Planck mass. Preliminary investigations suggest that this approach may be more promising