CPT and Superstring
  We discuss the possibility that CPT violation may appear as a consequence of microscopic decoherence due to quantum-gravity effects, that we describe using a density-matrix formalism motivated by our studies of non-critical string theory. The maximum possible order of magnitude of such decohering CPT-violating effects is not far from the sensitivity of present experiments on the neutral kaon system, and we review a simple parametrization for them. We also review a recent data analysis carried out together with the CPLEAR collaboration, which bounds any such decohering CPT-violating parameters to be $\lappeq 10^{-19}$ GeV. 
John Ellis, N.E. Mavromatos and D.V. Nanopoulos