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## Main Question or Discussion Point

i was thinking about propagators, and I've got bit of a silly question.

The amplitude for any given decay takes the form:

[tex]f(q^{2})=\frac{g^{2}}{q^{2}+M_{X}^{2}c^{2}}[/tex].

for EMAG decays, the Mx=0 (as we're dealing with photons), so the amplitude is just:

[tex]f(q^{2})=\frac{g^{2}}{q^{2}}[/tex],

Why do we not consider the propagator: [tex]\frac{1}{q^{2}}[/tex] when determining decay rates (we just say its proportional to the fine structure constant to power of the number of vertices)?

The amplitude for any given decay takes the form:

[tex]f(q^{2})=\frac{g^{2}}{q^{2}+M_{X}^{2}c^{2}}[/tex].

for EMAG decays, the Mx=0 (as we're dealing with photons), so the amplitude is just:

[tex]f(q^{2})=\frac{g^{2}}{q^{2}}[/tex],

Why do we not consider the propagator: [tex]\frac{1}{q^{2}}[/tex] when determining decay rates (we just say its proportional to the fine structure constant to power of the number of vertices)?