Invariant structure of the photon

The problem of photon wave function in coordinate space is entered upon proceeding from the Fourier analysis of the Electrodynamics already performed by Akhiezer and Berestetsky. Our approach refers solely to a definite free photon. The wave function in coordinate space is normalized as a result of selecting a single photon in momentum space and satisfies a Schroedinger-like equation. Probabilistic interpretation of wave function and relativistic invariance of wave equation are found to hold. A six-dimensional representation of the wave function complies with the parity conservation in electromagnetic interactions and points out a suggestive analogy between photon and 4-component neutrino. (author)