- #1
Qubix
- 82
- 1
Well, I was doing a problem the other day, inserting the complete interaction QED Lagrangian into the Euler-Lagrange equations, in order to obtain the field equation governing the interacting electromagnetic field, with the Dirac field. The problem is that, by doing so, I got the equation, but also a 1/4 factor in front. Any idea why this is ? (too lazy to latex the whole thing).
[tex] {\frac{-1}{4}} (∂^{α} ∂_{α} A^{μ}) = e {\overline{\Psi}}{\gamma}^{μ}{\psi} [/tex]
[tex] {\frac{-1}{4}} (∂^{α} ∂_{α} A^{μ}) = e {\overline{\Psi}}{\gamma}^{μ}{\psi} [/tex]