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1. ### Differential operator acting on scalar fields

Yeh sorry I did mean to put that A is a scalar field. Should be a bit more explicit about the problem I'm having as I wrote that last night after spending almost all my evening on it and I had given up. Basically the problem is to do with the klein gordon current with an electromagnetic field...
2. ### Differential operator acting on scalar fields

Homework Statement I really cannot seem to be able to follow the logic of how you would use the product rule when using 4 vector differential operator. ∂μ is the differential operator, Aμ is a scalar field and φ and φ* is it's complex conjugate scalar field. I have the answer, I'd just really...
3. ### Heisenburg Ferromagnetic Model

Homework Statement There are several parts to this question, however I could complete these parts. It is just an equation used in the prior part to the question that is need to solve this: If we define \begin{equation} \sigma_{n}^{-}=\sigma_{n}^{x}+i\sigma_{n}^{y} \end{equation} and with the...