  In recent papers [1,2], it has been shown that the presence of negative norm
states or negative frequency solutions are indispensable for a fully covariant
quantization of the minimally coupled scalar field in de Sitter space. Their
presence, while leaving unchanged the physical content of the theory, offers
the advantage of eliminating any ultraviolet divergence in the vacuum energy
[2] and infrared divergence in the two point function [3]. We attempt here to
extend this method to the interacting quantum field in Minkowski space-time. As
an illustration of the procedure, we consider the $\lambda\phi^4$ theory in
Minkowski space-time. The mathematical consequences of this method is the
disappearance of the ultraviolet divergence to the one-loop approximation. This
means, the effect of these auxiliary negative norm states is to allow an
automatic renormalization of the theory in this approximation.
