Srednicki begins his textbook on QFT by a handful of equations ("In order to prepare for QFT, you should recognize these:"). All of them I grasp but that one.
Obviously it smells like QM, but I've never seen that exact equation, whatever the A and H mean. Anyway it seems to reduce to just
, which is even more confusing.
So, anyone recognize something familiar in that equation? Thanks in advance.
PS: I'm pretty sure the answer is so simple as to mark me "noobie" up to the thousand and first generation...