content_image/310310.jpg content_image/310311.jpg content_image/310312.jpg content_image/310313.jpg content_image/310316.jpg
we then have 

<img src='content_image/310310.jpg'>

<img src='content_image/310311.jpg'>

Let’s now prove some nice relations regarding E and B that will be useful later on: transversality and orthogonality. To prove that ⃗ E is orthogonal to ⃗ k recall that A µ ∝ ( p ′ $^{µ}$/k · p $^{′}$) − ( p $^{µ}$/k · p ). Then 

Also 

since k 0 = ±| ⃗ k | , and we won’t be interested in the sign, we have that 

<img src='content_image/310312.jpg'>

<img src='content_image/310313.jpg'>

<img src='content_image/310316.jpg'>

