On the scalar product of short and long living states of neutral kaons   in the CPT invariant system
  This paper contains a detailed analysis of the properties of the scalar product of short and long living superpositions of neutral $|K_{0}>$, $|{\bar{K}}_{0}>$ mesons. It is shown for the exact effective Hamiltonian for neutral meson subsystem that the scalar product of its eigenvectors, which correspond with these short and long living superpositions, can not be real with the assumption of CPT conserved and CP violated. The standard conclusion obtained within the Lee-Oehme-Yang theory of neutral kaons is that in this case such a product should be real. 
K. Urbanowski