Screening of cosmological constant in non-local cosmology

Details Screening of cosmological constant in non-local cosmology Screening of cosmological constant in non-local cosmology

2011-08-10

arxiv.org/abs/1108.2112v2

Int.J.Mod.Phys.D21:1250006,2012

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

7 pages, 1 figure, LaTeX, V2:Some clarifications and references added

Scientific paper

We consider a model of non-local gravity with a large bare cosmological constant, $\Lambda$, and study its cosmological solutions. The model is characterized by a function $f(\psi)=f_0 e^{\alpha\psi}$ where $\psi=\Box^{-1}R$ and $\alpha$ is a real dimensionless parameter. In the absence of matter, we find an expanding universe solution $a\propto t^n$ with $n<1$, that is, a universe with decelarated expansion without any fine-tuning of the parameter. Thus the effect of the cosmological constant is effectively shielded in this solution. It has been known that solutions in non-local gravity often suffer from the existence of ghost modes. In the present case we find the solution is ghost-free if $\alpha>\alpha_{cr}\approx0.17$. This is quite a weak condition. We argue that the solution is stable against the includion of matter fields. Thus our solution opens up new possibilities for solution to the cosmological constant problem.

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