- #1
bananabandana
- 113
- 5
Homework Statement
Show that
$$ \mathcal{L} = -\frac{1}{4}F^{\mu \nu}F_{\mu \nu} = - \frac{1}{2}\partial^{\mu}A^{\nu}(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}) $$
Where $$ F^{\mu \nu} = \partial^{\mu}A^{\nu} - \partial^{\nu}A^{\mu} $$
Homework Equations
The Attempt at a Solution
$$ \mathcal{L} = -\frac{1}{4} F^{\mu \nu}F_{\mu \nu} = -\frac{1}{4}(\partial^{\mu}A^{\nu} - \partial^{\nu}A^{\mu})(\partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}) $$
Which expands out to:
$$ -\frac{1}{4} \bigg( \partial^{\mu}A^{\nu}\partial_{\mu}A_{\nu} - \partial^{\mu}A^{\nu}\partial_{\nu}A_{\mu} -\partial^{\nu}A^{\mu}\partial_{\mu}A_{\nu}+\partial^{\nu}A^{\mu}\partial_{\nu}A_{\mu} \bigg) $$
So if I just exchange indices on half of the terms, and then take out a factor, I get to the result I want... question is, how am I allowed to do that??