Kerr-Schild perturbations in higher derivative gravity theories in D dimensions

We study Kerr-Schild perturbations of a ghost-free, generic nonlocal gravity theory constructed from an infinite series of higher-derivative terms in D dimensions. The infinite series of higher-derivative terms are encoded by form factors, the forms of which can be restricted by requiring that the action remains perturbatively free of ghosts and tachyons around maximally symmetric backgrounds for transversetraceless fluctuations. To demonstrate this, we obtain field equations for the anti-de Sitter plane-wave metric in Kerr-Schild form, which yield linearized field equations for transverse-traceless spin-2 field. Using unitarity and consistency requirements, we obtain, as an example, the explicit derivation of nonlocal form factors in D dimensions.