Variable G and $Λ$: scalar-tensor versus RG-improved cosmology

Details Variable G and $Λ$: scalar-tensor versus RG-improved cosmology Variable G and $Λ$: scalar-tensor versus RG-improved cosmology

2004-10-11

arxiv.org/abs/astro-ph/0410260v1

Gen.Rel.Grav. 37 (2005) 521-539

Astronomy and Astrophysics

Astrophysics

25 pages, to be published in Gen. Rel. Grav. 2005

Scientific paper

10.1007/s10714-005-0040-0

We study the consequences due to time varying $G$ and $\Lambda$ in scalar-tensor theories of gravity for cosmology, inspired by the modifications introduced by the Renormalization Group (RG) equations in the Quantum Einstein Gravity. We assume a power-law scale factor in presence contemporarily of both the scalar field and the matter components of the cosmic fluid, and analyze a special case and its generalization, also showing the possibility of a phantom cosmology. In both such situations we find a negative kinetic term for the scalar field $Q$ and, possibly, an equation-of-state parameter $w_Q<-1$. A violation of dominant energy condition (DEC) for $Q$ is also possible in both of them; but, while in the first special case the $Q$-energy density then remains positive, in the second one we find it negative.

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