title: Scalar-field-dominated cosmology with a transient acceleration phase.
abstract: A new cosmological scenario driven by a slow rolling homogeneous scalar field whose exponential potential V(Phi) has a quadratic dependence on the field Phi in addition to the standard linear term is discussed. The derived equation of state for the field predicts a transient accelerating phase, in which the Universe was decelerated in the past, began to accelerate at redshift z approximately 1, is currently accelerated, but, finally, will return to a decelerating phase in the future. This overall dynamic behavior is profoundly different from the standard evolution of the cold dark matter model with a cosmological constant, and may alleviate some conflicts in reconciling the idea of a dark-energy-dominated universe with observables in String or M theory. Some theoretical predictions for the present scalar field plus dark matter dominated stage are confronted with cosmological observations in order to test the viability of the scenario.
authors.affiliation: Observatório Nacional, Rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, RJ, Brasil. fabiocc@on.br
authors.forename: F C
authors.initials: FC
authors.lastname: Carvalho
authors.forename: J S
authors.initials: JS
authors.lastname: Alcaniz
authors.forename: J A S
authors.initials: JA
authors.lastname: Lima
authors.forename: R
authors.initials: R
authors.lastname: Silva