Kavli Affiliate: Misao Sasaki
| First 5 Authors: Anamaria Hell, Anamaria Hell, , ,
| Summary:
We show that a single constrained scalar field with non-minimal coupling to
gravity can give rise to an accelerating Universe. First, we consider this
model in the absence of external matter. In the original Jordan frame, we show
that the dynamics of space-time is independent of the value of the cosmological
constant. We find analytical solutions, which include evolution from a
radiation dominated-like universe to an exponential expansion, as well as
evolution that starts with super-Hubble expansion and then relaxes towards an
exponential expansion of the Universe. We also show that the scalar
perturbations of this theory are well-behaved in the Jordan frame. Furthermore,
we perform the formulation of the corresponding theory in the Einstein frame,
and analyse the corresponding accelerating solutions. Second, we consider the
model in the presence of matter. We find that the matter does not affect the
evolution of the universe if minimally coupled to the scalar field. In other
words, in the Jordan frame, in order to influence the evolution of the
space-time, the matter should be non-minimally coupled to the constrained
scalar, while it may be minimally coupled to gravity. We show that in this
case, the solutions are similar to the free case, and, in addition, allow for
the phantom-like equation of state. Finally, we consider the theory in the
minimal frame, in which the matter is minimally coupled to both gravity and the
constrained scalar, and show that among other possibilities, the phantom-like
equation of state can still be satisfied in this minimal frame.
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