Stability of the flat space in quasi-Riemannian theories of gravity (Q1116478)

The most general action linear in curvature and quadratic in torsion for a quasi-Riemannian theory with tangent space group \(SO(1,N-1)\times SO(M)\) is obtained. Stability of the flat space solution of the field equations is studied, by calculating the massless and massive spectrum of excitations. It is shown that some very stringent conditions must be imposed on the parameters of the action in order to avoid instabilities.