  We show that the combined minimal and non minimal interaction with the
gravitational field may produce the generation of a cosmological constant
without self-interaction of the scalar field. In the same vein we analyze the
existence of states of a scalar field that by a combined interaction of minimal
and non minimal coupling with the gravitational field can exhibit an unexpected
property, to wit, they are acted on by the gravitational field but do not
generate gravitational field. In other words, states that seems to violate the
action-reaction principle. We present explicit examples of this situation in
the framework of a spatially isotropic and homogeneous universe.
