= Higgs boson coupling to Z bosons
{c}
{title2=$\mathcal L_{HZ}=m_Z^2HZ_\mu Z^\mu/v+m_Z^2H^2Z_\mu Z^\mu/(2v^2)$}
= Higgs boson couplings to Z bosons
{c}
{synonym}
The neutral vector mass term is $\frac12m_Z^2Z_\mu Z^\mu(1+H/v)^2$. Expanding it gives the cubic $HZZ$ and quartic $HHZZ$ interactions in <unitary gauge>. Differentiating the action with respect to identical fields gives <Feynman rules> $2im_Z^2g_{\mu\nu}/v$ and $2im_Z^2g_{\mu\nu}/v^2$. A single $Z$ does not couple to two copies of the real neutral radial <Higgs boson> through an elementary vertex.
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