Localization of photons in quantum field theory

A solution is proposed to the long-standing problem of localization of photons in configuration space in quantum field theory which has been clearly indicated by an abundance of experimental results obtained in very recent years and earlier ones originating at the beginning of this century. The analysis is based directly on the actual physical situation where photons travel between emitters and detectors, and the solution is dictated by the consistency requirement of the completeness relation associated with a unitarity expansion in configuration space for a correct probabilistic interpretation. An explicit expression for the amplitude for a photon excitation to travel from one time-space coordinate to another is derived from this unitarity expansion. Finally, detailed numerical and very precise estimates are obtained on the localization of photon excitations in relation to the constancy of the speed of light when the photon excitations travel large distances after their emission. This is a generalization of a recent publication [Hadronic J. 11, 263 (1988)] by the author dealing with strictly massive particles