Feynman Propagators: Invariant Amplitude vs Loop Integrals

[ryanwilk]

Hi, this is probably very simple but what is the difference between these two Feynman propagators:

\frac{i}{q^2-m^2}
\frac{i(p/+m)}{p^2-m^2}

E.g. Is one used for the invariant amplitude and the other for loop integrals? Or is one for a fermion and the other for a boson? =s

Thanks!

 

[Vanadium 50]

The top one is for a scalar, the bottom one for a spin-1/2 particle.

 

[ryanwilk]

Thank you!