Ward-Takahashi Identity · Gauge Symmetry Constrains the Vertex
unseel.com · kμ Γμ = S⁻¹(p+k) − S⁻¹(p) · U(1) current conservation
Identity gap
Z₁ vs Z₂
phase
Electron line (momentum p)
Photon momentum k / vertex Γμ
Inverse propagator S⁻¹
Identity balanced / Z₁ = Z₂
Unseel.com · The Ward-Takahashi Identity: Gauge Symmetry Constrains the Vertex