  In the present work we revisit a model consisting of a scalar field with a
quartic self-interaction potential non-minimally (conformally) coupled to
gravity [1]. When the scalar field vacuum is in a broken symmetry state, an
effective gravitational constant emerges which, in certain regimes, can lead to
gravitational repulsive effects when only ordinary radiation is coupled to
gravity. In this case, a bouncing universe is shown to be the only cosmological
solution admissible by the field equations when the scalar field is in such a
broken symmetry state.
