 Renormalized quartic scalar vertex

The renormalized quartic scalar vertex ${\Gamma }_R^{(4)}$ is the four-field proper vertex expressed in terms of renormalized fields and parameters. For a quartic interaction, its leading contribution is the tree-level coupling; loop corrections and counterterms modify its dependence on external momenta and the chosen renormalization scale.

A renormalization condition can define the coupling by prescribing the vertex at a specified momentum configuration. Changing that scale changes the coupling according to its renormalization-group beta function, while consistently computed physical predictions remain unchanged to the retained accuracy. This proper vertex is one-particle irreducible; it is not an arbitrary four-point correlation function with external propagation left attached. A comparison must state field normalization, momentum convention and whether an overall factor of $i$ is included in the definition.