Quasiclassical solutions of the Klein-Gordon equation in a space-time with closed time-like curves

A formulation of the Cauchy problem for the Klein-Gordon equation in a space-time with a wormhole is studied. It is shown that if closed time-like curves pass through the Cauchy surface, then a global solution exists in the high-frequency (quasiclassical) limit only if the initial data satisfy nonlocal consistency conditions. In the simplest case these conditions determine a discrete spectrum of frequencies (energies of a quasiclassical scalar particle). Zh. éksp. Teor. Fiz. 113, 3–11 (January 1998)