Counting ghosts in the “ghost-free” non-local gravity
Ilya L. Shapiro (Departamento de Física, ICE, Universidade Federal de Juiz de Fora, Campus Universitário, Juiz de Fora, MG, 36036-330, Brazil, Tomsk State Pedagogical University, Tomsk State University, Tomsk, Russia, Département de Physique Théorique, Center for Astroparticle Physics, Université de Genève, 24 quai Ansermet, Genève 4, CH-1211, Switzerland)
In the recently proposed non-local theory of quantum gravity one can avoid massive tensor ghosts at the tree level by introducing an exponential form factor between the two Ricci tensors. We show that at the quantum level this theory has an infinite amount of massive unphysical states, mostly corresponding to complex poles.