Tree (bare)
Structure
A single propagator line or a single vertex point with attached legs.
Where it appears
The bare photon propagator $-ig_{\mu\nu}/k^2$, the bare electron propagator $i(\not{p}+m)/(p^2-m^2)$, and the bare vertex $-ie\gamma^\mu$.
A single propagator line or a single vertex point with attached legs.
The bare photon propagator $-ig_{\mu\nu}/k^2$, the bare electron propagator $i(\not{p}+m)/(p^2-m^2)$, and the bare vertex $-ie\gamma^\mu$.