A New Model of Nonlocal Modified Gravity
  We consider a new modified gravity model with nonlocal term of the form $R^{-1} \mathcal{F}(\Box) R. $ This kind of nonlocality is motivated by investigation of applicability of a few unusual ans\"atze to obtain some exact cosmological solutions. In particular, we find attractive and useful quadratic ansatz $\Box R = q R^{2}.$ 
Ivan Dimitrijevic, Branko Dragovich, Jelena Grujic and Zoran Rakic
hep-th gr-qc