Screening of cosmological constant in non-local cosmology

Understand

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.