In Quantum Electrodynamics (QED), the interaction between charged scalar particles is described by a transition amplitude derived from four-vector currents coupled via photon exchange propagators within the Klein-Gordon formalism. The theoretical framework establishes that this process must satisfy global energy and momentum conservation, enforced mathematically by Dirac delta functions arising from Fourier integration of plane wave states in infinite volume. Consequently, while the free electromagnetic field possesses zero mass (q²=0), interacting photons acquire an effective inverse-mass-like propagator factor ($1/q^2$) mediating forces between matter currents without implying a violation of energy conservation for observable macroscopic systems.
In Quantum Electrodynamics (QED), the interaction between charged scalar particles is described by a transition amplitude derived from four-vector currents coupled via photon exchange propagators wit…