= Charge assignments for a cubic complex-scalar interaction
{title2=$\phi^2\Phi:\quad2q_\phi+q_\Phi=0$}
The interaction $-\tfrac12(h\phi^2\Phi+h^*\phi^{\dagger2}\Phi^\dagger)$ is invariant under a <global phase symmetry> precisely when the displayed charge relation holds. With $q_\phi=1$, a heavy <particle> annihilated by $\Phi$ has charge $-2$, so its allowed <decay channel> is $\Phi\to\bar\phi\bar\phi$. The reverse heavy <antiparticle> decays into $\phi\phi$. Crossing only one heavy external state changes the exchange channel of mixed-species <quantum scattering>.
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