De Sitter universe in nonlocal gravity
De Sitter universe in nonlocal gravity
A nonlocal gravity model, which does not assume the existence of a new dimensional parameter in the action and includes a function $f({\ensuremath{\square}}^{\ensuremath{-}1}R)$, with $\ensuremath{\square}$ the d'Alembertian operator, is considered. The model is proven to have de Sitter solutions only if the function $f$ satisfies a certain second-order linear differential …