A New Quantum Field Theory Approach to the Description of Finite-Time Processes

Within the quantum field theory, a new approach to the description of processes taking place at finite space-time intervals is considered. It is based on the Feynman diagram technique in the coordinate representation, in which the transition to the momentum representation is modified in accordance with the existing experimental situation. As a result, the Feynman propagator of particles in the momentum representation changes, while the other Feynman rules remain unchanged. In this approach, wave packets are not used and the initial and final states of particles are described by plane waves, which significantly simplifies the calculations. By example of the decay of an unstable particle and neutrino oscillations, it is shown how the differential probabilities of these processes can be found and that the results obtained agree with the expected ones.