Photon Propagator

1
Photon Propagator
x
Positive frequencies propagate forward in time.
In end, must take limit as e?0
2
Scattering Matrix
3
Scattering Matrix (continued)
4
Scattering Matrix (continued)
5
Cross Section
Lab frame
Where Ef and pf are determined by the scattering
angle ?
6
Matrix Element
Likewise
7
Check for Coulomb Scattering
Same as Coulomb case
8
Contract Tensors
9
Real Protons
0 when contracted with symmetric lepton tensor.
Therefore set to zero
Current conservation
10
Real Proton compared to Dirac Proton
Real
Dirac
Dirac
11
Contract Real Proton with Lepton Tensor
Since
(Current conservation on lepton vertex)
Likewise, since