Feynman Diagrams For Pedestrians - Herbstschule Maria Laach
Feynman Diagrams For Pedestrians - Herbstschule Maria Laach
Feynman Diagrams For Pedestrians - Herbstschule Maria Laach
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
• NB: this is not what happens in the standard model, where the mass comessolely from the coupling to the Higgs sector and a gauge freedom remains.However (102) is in lowest order equivalent to the Higgs mechanism in unitaritygauge• NB: propagators and external states are universal and models differ only in theparticle content and interaction vertices!3.2 <strong>Feynman</strong> Rulesexternal spin-1/2 particles:incoming:outgoing:pp⇐⇒ · · · u(p)⇐⇒ ū(p) · · ·(103a)(103b)external spin-1/2 anti particles:incoming:outgoing:pp⇐⇒ ¯v(p) · · ·⇐⇒ · · · v(p)(103c)(103d)external spin-1 particles:incoming:outgoing:kk⇐⇒ ɛ µ (k)⇐⇒ ɛ ∗ µ(k)(103e)(103f)• internal particles and anti particles with sign of momentum relative to the arrow(i. e. charge) direction:spin-1/2:p⇐⇒i/p − m + iɛ(104a)spin-1 (m = 0):k⇐⇒ −ig µν + i(1 − ξ) k µk νk 2 +iɛk 2 + iɛ(104b)• finallyspin-0:p⇐⇒ip 2 − m 2 + iɛ(105)∵ the S-matrix always contains an uninteresting diagonal piece (no interaction) andthe global momentum conservation δ-distributionS = 1 + (2π) 4 δ 4 (p 1 + p 2 − q 1 − q 2 . . . − . . . q n )iT (106)∴ we can focus on T20