External Particles

With each external line one has to assoicate the following factors.

Spin 1/2: For each fermion or antifermion line entering the graph include the spinor

$$\sqrt{\frac{m}{EV}} u(p,s) \quad\textrm{or}\quad \sqrt{\frac{m}{EV}} v(p,s)$$ (7.372)

and for spin-1/2 particles leaving the graph, the spinor

$$\sqrt{\frac{m}{EV}} \overline{u}(p^\prime,s^\prime) \quad\te... ...or}\quad \sqrt{\frac{m}{EV}} \overline{v}(p^\prime,s^\prime) .$$ (7.373)

Spin 0: For each boson assign a factor

$$\sqrt{\frac{m}{EV}} .$$ (7.374)

Photons: For each photon entering the graph include a polarization vector

$$\varepsilon_\mu(k,\lambda)$$ (7.375)

and for photons leaving the graph the vector

$$\varepsilon_\mu^*(k^\prime,\lambda^\prime) .$$ (7.376)