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I need some help concerning the interpretation of propagators and Feynman diagrams.

The free fermion propagator is given by the contraction of two fields $\psi(x),\bar\psi(y)$:

$D_F(x-y)=T\{\psi(x)\bar\psi(y)\}$

In this notation, the arrow in the Feynman diagram linking $x$ and $y$ will go from $x$ to $y$ or the opposite?

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    $\begingroup$ Where the arrow points is a matter of convention. Doesn't matter what you do, as long as you are consistent. $\endgroup$ – ACuriousMind Nov 9 '15 at 17:09
  • $\begingroup$ Can you please be more explicit? If we denote an anti-particle with an arrow going in the opposite direction of the momentum, what is the answer? $\endgroup$ – AxelAE Nov 9 '15 at 17:26

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