Gauge Invariance, Lorentz Covariance, and Current Correlation Functions

Publisher Website
Google Scholar
Abstract
Current correlation functions are defined by means of the response of a system to variations in an external potential. These functions contain, in addition to the time-ordered product of current operators, extra terms that are related to the equal-time noncommutativity of charge and current densities. Although the time-ordered product is not Lorentz-covariant, the requirement of gauge invariance is shown to imply the Lorentz covariance of the entire current correlation function.