There are two <tree-level Feynman diagrams> for <Compton scattering>: an $s$-channel ordering in which the electron first absorbs the incoming photon, with internal momentum $p+q$, and a crossed $u$-channel ordering in which it first emits the outgoing photon, with internal momentum $p-q'$.

\Image[/media/past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2019/iii/paper-301-compton-diagrams.png]
{title=Tree-level Compton-scattering diagrams}
{description=The two orderings of photon absorption and emission give the electron-exchange s-channel and u-channel diagrams.}
{height=430}

Solution

Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 301 / 3 / iv / b / Solution

 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2019/iii/paper-301/3/iv/b/solution