Test of the Equivalence Principle from K Physics
  A violation of the equivalence principle (VEP) in the Kaon system can, in principle, induce oscillations between $K^\circ$ and $\overline{K^\circ}$ in a manner that need not violate CPT conservation. We show that such a CPT-conserved VEP mechanism could be clearly tested experimentally through the energy dependence of the $K_L-K_S$ mass difference and discuss constraints imposed by present experiments. 
T. Hambye, R.B. Mann and U. Sarkar