The Abraham Zelmanov Journal
The journal for General Relativity, gravitation and cosmology
Cosmological Models in the Generalized Einstein Action
We have studied the evolution of the Universe in the generalized Einstein action of the form R + βR2, where R is the scalar curvature and β = const. We have found exact cosmological solutions that predict the present cosmic acceleration. These models predict an inflationary de-Sitter era occurring in the early Universe. The cosmological constant (Λ) is found to decay with the Hubble constant (H) as, Λ ∝ H 4. In this scenario the cosmological constant varies quadratically with the energy density (ρ), i.e., Λ ∝ ρ2. Such a variation is found to describe a two-component cosmic fluid in the Universe. One of the components accelerated the Universe in the early era, and the other in the present era. The scale factor of the Universe varies as a ~ tn, n = 1/2 in the radiation era. The cosmological constant vanishes when n = 4/3 and n = 1/2. We have found that the inclusion of the term R2 mimics a cosmic matter that could substitute the ordinary matter. It is also equivalent to having a bulk viscosity of ordinary cosmology.
Ref: The Abraham Zelmanov Journal, 2009, volume 2, pages 3-10
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The Abraham Zelmanov Journal is an annually issue scientific journal registered with the Royal National Library of Sweden.