Cosmological Acceleration Through Transition to Constant Scalar Curvature

As shown by Parker and Raval, quantum field theory in curved spacetime gives a possible mechanism for explaining the observed recent acceleration of the universe. This mechanism is consistent with a zero cosmological constant, and causes the universe to make a transition to an accelerating expansion in which the scalar curvature, R, of spacetime remains constant. We show that this model agrees very well with the current observed type-Ia supernova (SNeIa) data. There are no free parameters in this fit, as the relevant observables are determined independently by means of the current cosmic microwave background radiation (CMBR) data. We also give the predicted curves for number count tests and for the ratio, w(z), of the dark energy density to its pressure, as well as for dw(z)/dz versus w(z). These curves differ significantly from those obtained from a cosmological constant, and will be tested by planned future observations. Subject headings: cosmic microwave background — cosmological parameters — cosmology: observations — cosmology: theory — gravitation — supernovae: general