Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

In the equation (1.18) they omitted the translation vector $a^\mu$, but why?

share|cite|improve this question
Am I correct that you added the a here? Because the index is wrong, you shouldn't have three mus in one expression, it has to be a sigma – Noldig Feb 14 '13 at 15:24
up vote 5 down vote accepted

Because a constant vector (like the translation vector) is annihilated by the differential operator $\partial^\mu$.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.