246 research outputs found
Dynamical analysis and cosmological viability of varying and cosmology
The cosmological viability of varying and cosmology is discussed by determining the cosmological eras provided
by the theory. Such a study is performed with the determination of the critical
points while stability analysis is performed. The application of
Renormalization group in the ADM formalism of General Relativity provides a
modified second-order theory of gravity where varying plays
the role of a minimally coupled field, different from that of Scalar-tensor
theories, while is a potential term. We find that the theory provides two de Sitter phases
and a tracking solution. In the presence of matter source, two new critical
points are introduced, where the matter source contributes to the universe. One
of those points describes the CDM cosmology and in order for the
solution at the point to be cosmologically viable, it has to be unstable.
Moreover, the second point, where matter exists, describes a universe where the
dark energy parameter for the equation of state has a different value from that
of the cosmological constant.Comment: 13 pages, 4 figures, discussion improved, to appear in EPJ
Analytic Solution of the Starobinsky Model for Inflation
We prove that the field equations of the Starobinsky model for inflation in a
Friedmann-Lema\^{\i}tre-Robertson-Walker constitute an integrable system as the
field equations pass the singularity test. The analytical solution in terms of
a Painlev\'{e} Series for the Starobinsky model is presented for the case of
zero and nonzero spatial curvature. In both cases the leading-order term
describes the radiation era provided by the corresponding higher-order theory.Comment: 5 pages, references added, to appear in EPJ
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