  We compute the spectrum of scalar models with a general coupling to the
scalar curvature. We find that 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, we
are able to define an Einstein frame, where the dynamics of the massless spin-2
graviton is the one associated with the Einstein-Hilbert action. We also
explore the interactions of all these degrees of freedom in the mentioned
frame, since part of the coupling structure can be anticipated by geometrical
arguments.
