Composite operator mixing (${\mathcal{O}}_B=Z{\mathcal{O}}_R$)

Renormalization can relate bare operators to a matrix of renormalized operators, ${\mathcal{O}}_{i,B}=Z_{ij}{\mathcal{O}}_{j,R}$. The corresponding anomalous dimension matrix acts on each insertion slot in the Callan-Symanzik equation.