# Dealing with more complicated tree level feynman diagrams

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

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?

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