Scalar-field-dominated cosmology with a transient accelerating phase
  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 $z \sim 1$, is currently accelerated, but, finally, will return to a decelerating phase in the future. This overall dynamic behavior is profoundly different from the standard $\Lambda$CDM evolution, and may alliviate some conflicts in reconciling the idea of a dark energy-dominated universe with observables in String/M-theory. The theoretical predictions for the present transient scalar field plus dark matter dominated stage are confronted with cosmological observations in order to test the viability of the scenario. 
F.C. Carvalho (on), J.S. Alcaniz (on), J.A.S. Lima (IAG), R. Silva   (UERN)