EXPANSIONS OF NONSYMMETRICAL GRAVITATIONAL THEORIES ABOUT A GR BACKGROUND

A large number of Lagrangian-based non-Riemannian geometrical theories of gravitation are consistently generated by the method of algebraic extension. Of this number, only two possess a physically viable excitation spectrum (particle content) when expanded about Minkowski spacetime. They are NGT (non-symmetric gravitational theory) and AHG (algebraically extended Hilbert gravity). We undertake the linear expansion of these two theories about an arbitrary vacuum general relativistic background spacetime. AHG fails to remain ghost free upon a non-flat background while NGT preserves its symmetries and particle content. NGT is the only AE Hermitean theory remaining in contention as an alternative theory to general relativity.