Nonminimal scalar-tensor theories

We compute the spectrum, mixing and interaction structure of scalar models with a general coupling to the scalar curvature. As it is well known the perturbative states of these theories are given by two massive spin-0 modes in addition to one massless spin-2 state. This latter mode can be identified with the standard graviton field. Indeed, it is possible to define an Einstein frame, where the dynamics of the massless spin-2 graviton is the one associated with the Einstein-Hilbert action. We explore systematically the interactions of all these degrees of freedom in the mentioned frame, since part of the coupling structure can be anticipated by geometrical arguments.