# Klein-Gordon propagator

1. Feb 7, 2008

### WarnK

1. The problem statement, all variables and given/known data
2. Relevant equations
Show that the KG propagator
$$G_F (x) = \int \frac{d^4p}{(2\pi)^4} e^{-ip.x} \frac{1}{p^2-m^2+i\epsilon}$$
satsify
$$(\square + m^2) G_F (x) = -\delta(x)$$

3. The attempt at a solution
I get
$$(\square + m^2) G_F (x) = - \int \frac{d^4p}{(2\pi)^4} (p^2-m^2) e^{-ip.x} \frac{1}{p^2-m^2+i\epsilon}$$
but where do I go from there?

Last edited: Feb 7, 2008
2. Feb 7, 2008

### pam

Cancel the numerate and denominator p^2-m^2.
The i epsilon is just a direction how to take the contour, and is negligible here.
The remaining integral is \delta^4.

3. Feb 7, 2008

### malawi_glenn

how does (p^2-m^2)/(p^2-m^+i*epsilon) cancel?

I would try to do the limit of epsilon -> 0+

Last edited: Feb 7, 2008
4. Feb 8, 2008

### pam

That's what
"The i epsilon is just a direction how to take the contour, and is negligible here."
means.