Stability of de Sitter Solutions in Non-local Cosmological Models
  A non-local gravity model, which includes a function $f(\Box^{-1} R)$, where $\Box$ is the d'Alembert operator, is considered. For the model with an exponential $f(\Box^{-1} R)$ de Sitter solutions are explored, without any restrictions on the parameters. Using Hubble-normalized variables, the stability of the de Sitter solutions is investigated, with respect to perturbations in the Bianchi I metric, in the case of zero cosmological constant, and sufficient conditions for stability are obtained. 
E. Elizalde, E. O. Pozdeeva, S. Yu. Vernov
gr-qc astro-ph.CO hep-th math-ph math.MP