Causal loop in the theory of relative locality
  We find that relative locality, a recently proposed Planck-scale deformation of special relativity, suffers from the existence of causal loops. A simple and general construction of such on-shell loop processes is studied. We then show that even in one of the weakest deformations of the Poincar\'e group in relative locality, causality can be violated. 
Lin-Qing Chen
gr-qc hep-th