 Solution

ID: past-exam-of-the-quantum-field-theory-course-of-the-university-of-oxford/2021/1/b/iii/solution

For

Ψ (p_{1}) \to χ (p_{2}) + ϕ (p_{3})

p_{1} = p_{2} + p_{3}

. Its invariant decay amplitude is

i M_{s_{1} s_{2}} = - i g \overset{u}{ˉ}_{χ}^{s_{2}} (p_{2}) u_{Ψ}^{s_{1}} (p_{1}) .

The solid arrow passes from the incoming

Ψ

to the outgoing

χ

; the dashed outgoing line carries

p_{3}

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