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, which differs in its dynamics from quintessence models, causes the universe to make a transition to an accelerating expansion in which the scalar curvature, R, of spacetime remains constant. This transition occurs despite the fact that we set the renormalized cosmological constant to zero. We show that this model agrees very well with the current observed type-Ia supernova (SNe-Ia) 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 pressure to its density, 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.Comment: 31 pages, 7 figures; to appear in ApJ. Corrected numerical results; described quantum basis of theory; 18 references added; 2 figures adde

Sudden Gravitational Transition

We investigate the properties of a cosmological scenario which undergoes a gravitational phase transition at late times. In this scenario, the Universe evolves according to general relativity in the standard, hot big bang picture until a redshift z≲1. Nonperturbative phenomena associated with a minimally-coupled scalar field catalyzes a transition, whereby an order parameter consisting of curvature quantities such as R2, RabRab, RabcdRabcd acquires a constant expectation value. The ensuing cosmic acceleration appears driven by a dark-energy component with an equation-of-state w\u3c−1. We evaluate the constraints from type 1a supernovae, the cosmic microwave background, and other cosmological observations. We find that a range of models making a sharp transition to cosmic acceleration are consistent with observations

A Sudden Gravitational Transition

We investigate the properties of a cosmological scenario which undergoes a gravitational phase transition at late times. In this scenario, the Universe evolves according to general relativity in the standard, hot Big Bang picture until a redshift z \lesssim 1. Non-perturbative phenomena associated with a minimally-coupled scalar field catalyzes a transition, whereby an order parameter consisting of curvature quantities such as R^2, R_{ab}R^{ab}, R_{abcd}R^{abcd} acquires a constant expectation value. The ensuing cosmic acceleration appears driven by a dark-energy component with an equation-of-state w < -1. We evaluate the constraints from type 1a supernovae, the cosmic microwave background, and other cosmological observations. We find that a range of models making a sharp transition to cosmic acceleration are consistent with observations.Comment: 8 pages, 8 figures; added reference