ИСТИНА

A new approach to the quantum field-theoretical description of processes passing at finite space–time intervals is developed. To this end, the standard perturbative S-matrix formalism is modified so that it can be used for calculating the amplitudes of the processes passing at finite distances and finite time intervals. The new formalism is based on the Feynman diagram technique in the coordinate representation supplemented with modified rules for passing to the momentum representation reflecting specific experimental situations. Accordingly, only the particle propagators in the momentum representation are modified, while the standard Feynman rules in the momentum representation remain unchanged. The processes of a displaced decay of an unstable particle and of neutral kaon and neutrino oscillations are used to show that the developed approach correctly reproduces the results of the standard quantum-mechanical description. An important feature of the approach is the fact that it uses only the particle mass eigenstates and plane waves, which essentially simplifies the calculations of the amplitudes.