Wave-function renormalization ($Z_{\varphi }$)

Wave-function renormalization rescales a field so that its kinetic term or propagator residue has the chosen normalization. Its scale dependence gives the field's anomalous dimension.

In scalar electrodynamics with photon propagator $-i[g_{\mu \nu }-(1-\xi )l_{\mu }{l}_{\nu }/l^2]/(l^2+i0)$ and dimensional regularization $d=4-2ϵ$, the minimal subtraction scheme gives $Z_{\varphi }=1+e^2(3-\xi )/(16{\pi }^2ϵ)+O(e^4)$. For an external four-momentum $p$, expand the exchange numerator as $4p^2-4\xi p\cdot l+\xi l^2-4(1-\xi )(p\cdot l{)}^2/l^2$. The logarithmic ultraviolet poles of the scalar, vector and tensor integrals give the $p^2$ coefficient $4-2\xi -(1-\xi )=3-\xi$. A massless photon tadpole integral does not change it. The scalar QED Ward identity gives the same vertex renormalization constant.

Canonical field normalization rescales a field so that its kinetic term has unit coefficient. For a chiral superfield with $K=Z{\Phi }^{†}\Phi$, the change ${\Phi }_c=Z^{1/2}\Phi$ turns holomorphic superpotential parameters into canonical parameters $m_c=m/Z$ and $g_c=g/Z^{3/2}$.

For $\varphi =\kappa (v+h+ib)$, the real fluctuation kinetic terms are $-{\kappa }^2[(\partial h{)}^2+(\partial b{)}^2]$. The same $v$ labels a Minimum of $V=\lambda (|\varphi {|}^2-v^2/2{)}^2/4$ and gives canonically normalized real fields exactly when ${\kappa }^2=1/2$. This condition also makes $G=\partial \cdot A-\xi gvb$ cancel the gauge-scalar derivative mixing: its coefficient is $(2{\kappa }^2-1)gvA\cdot \partial b$. Changing the normalization of the fields without changing the gauge function need not be a conventional diagonal $R_{\xi }$ gauge.