Brans-Dicke Cosmology Corrected for a Quantum Effect due to the Scalar-Matter Coupling

Cosmological solutions of the Brans-Dicke theory are investigated by including a quantum effect coming from 1-loop correction of matter fields that couple to the scalar field. As the most serious result we face a cosmological constant'' in the original conformal frame which is shown to be physical’’ after a careful analysis of the time variable employed in any of the conventional approaches. We find an attractor'' solution featuring no expansion during the radiation-dominated eras. To evade this unacceptable consequence, we suggest to modify one of the fundamental premises of the model, rendering the scalar field almost invisible.‘’