b
= b
{scope}
\Image[/past-exam-of-the-quantum-field-theory-course-of-the-university-of-oxford/2020-yukawa-tree-channels.png]
{title=Momentum-labelled tree diagrams for the three Yukawa scattering processes. Solid arrows show fermion flow; dashed lines are scalar exchange. Each row contains every allowed tree channel for that process.}