Hello I have been having trouble understanding equation 14.25 in Bjorken and Drell "Relativistic Quantum Fields" and how exactly it gets to it. Also I would like to explicitly find/derive what the operator gauge function is. Can anyone help please?
Definitely want to do theoretical. Hate experimental. No interest in device orientated research more into the gritty theoretical modelling. Any idea what the top american universities would be for that?