General Sum Rules and the Form of the Equal-Time Commutator
M. O. Taha · Physical Review · 1967
Using a method introduced in a previous paper, we define covariant functions corresponding to the retarded product and the equal-time commutator. From these we obtain general sum-rule identities, employing three independent infinite limits. These identities considerably limit the form of the equal-time commutator. The simplest form consistent with the general covariance properties is discussed.