Momentum-support exclusion for Wilsonian bridge diagrams
= Momentum-support exclusion for Wilsonian bridge diagrams
{title2=$C_>*\phi_<=0$}
If a bridge is the only line carrying momentum away from a low external field, tadpole pairs do not change its momentum and the <shell-restricted scalar propagator> has zero support there. A bridge attached to a product such as $\phi_<^3$ can survive because the sum of three low momenta can enter the shell. This matters before a local <derivative expansion>.