A Unique Theory of Gravity and Matter

The author has previously suggested that the ground state for 4-dimensional quantumgravity can be represented as a condensation of non-linear gravitons connected by Dirac strings.In this note we suggest that the low-lying excitations of this state can be described by a quasi-topological action of the form ∫d 13 z F4 F5 F4 , corresponding to a trilinear coupling of solitonic 8-branes and 7-branes. It is shownthat when the excitations associated with F5 are neglected, the effective action can beinterpreted as a theory of conformal gravity in four dimensions. This in turn suggests that ordinarygravity as well supersymmetric matter and phenomenological gauge symmetries arise from thespontaneous breaking of topological invariance. The possibly deep mathematical significance ofthis theory is also noted. 1999 Elsevier Science Ltd.