# Renormalization of field strength

I'm revisiting the elementary algorithms of renormalization that are taught in a classroom setting and find that the procedure taught to students is as follows:

1. Write down the bare Lagrangian: $\mathcal{L}_0$
2. Renormalize the field strengths: $\phi_0\rightarrow Z^{1/2}\phi_r$
3. Renormalize coupling constants: e.g. $Z^2\lambda_0\rightarrow Z_\lambda \mu^{2\epsilon}\lambda_R$
4. For perturbation theory rewrite $Z=1+\delta$, where $\delta$'s are counterterms.

I have thought long and hard about steps 2 and 3 (especially in the context of operator renormalization), and have come to the following conclusions which I would like verified.

In step 3, the renormalization of coupling constants is actually the renormalization of the operator product multiplying the coupling constant. And, in step 2, when they renormalize the field strength, it is not the renormalization of a single operator; they are actually renormalizing another composite operator: the kinetic term $\partial_\mu\phi\,\partial^\mu\phi$. The renormalization of a single operator $\phi$ actually corresponds to tadpoles, the one-point function.

Am I interpreting this correctly?

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Yes, the source is the kinetic term, so it is the normalization of a composite operator, but it is the same as rescaling $\phi$ by Z, so the use the language of normalizing the field strength. The translation shift of a single operator $\phi$ corresponds to tadpoles, and rescaling $\phi$ is only a translation shift if $\phi$ has a VEV, and then the tadpole formalism is annoying in the region where you need a Maxwell construction. There was a question on tadpoles and effective action which I didn't answer yet, because of the Maxwell construction issue for the effective action. – Ron Maimon Nov 4 '12 at 2:21
Thanks for the answer. And, so like $\phi$, can I expect any composite operator to have a multiplicative and an additive component to its renormalization? that is, $\mathcal{O}\rightarrow Z\mathcal{O}+Y$ ? – QuantumDot Nov 4 '12 at 2:47
Only a multiplicvative one, one constant per monomial. – Arnold Neumaier Nov 19 '12 at 9:57