Suppose I have a 2 -> 4 body process of the form

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Where all particles are scalar $\phi$ of mass $m$, dirac fermion $\chi$ of mass $M$ with interaction lagrangian $g\overline{\chi}\chi \phi$ . How does one order the calculation correctly to compute this amplitude, given that there are the three propagators to consider here? does ordering matter in the toy case?

  • $\begingroup$ Well, in principle you just use the Feynman rules. If you're confused about how to use them, show us what you've tried. $\endgroup$ – knzhou Feb 9 at 17:07
  • $\begingroup$ So, by cutting the diagram into three components (two 2->2 scattering and the fermion propagator), $-iM =[ \bar{u}(q)gu(p_1) \Delta(p_1-q,m) \times \bar{u}(p_6)gu(p_2) ]\times S(q,M) \times[ \bar{u}(p_3)gu(q) \times \Delta(p_3-q,m) \times \bar{u}(p_4)gv(p_5)]$ $\endgroup$ – MKF Feb 9 at 17:28
  • $\begingroup$ You have 8 fermion wave functions but there are only 6 external legs $\endgroup$ – MannyC Feb 9 at 18:35

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