Mass independent Klein Gordon equation

We transform the Klein–Gordon equation into a mass-independent form that treats space–time more symmetrically. The mass-independent Klein–Gordon equation (MIKE) is first order in a variable that plays the role of time, the approach taken in parametric time formulations. MIKE is useful for studying the effects of noise because we can borrow techniques from the theory of quantum open systems, where first order master equations often appear. Moreover, we can maintain space–time symmetry while carrying out calculations. Specifically, we use MIKE to study the noisy Feynman propagator, a correlation function of two fields in the presence of noise. One characteristic of the Feynman propagator (its sign) is important to ensure that probabilities properly range from zero to one. We find that the sign is preserved in the presence of electromagnetic noise.