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SE tensor for scalar field

  • Thread starter BillKet
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  • #1
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Homework Statement


Show that if the Lagrangian only depends on scalar fields ##\phi##, the energy momentum tensor is always symmetric: ##T_{\mu\nu}=T_{\nu\mu}##

Homework Equations


##T_{\mu\nu}=\frac{\partial L}{\partial(\partial_\mu\phi)}\partial_\nu\phi-g_{\mu\nu}L##

The Attempt at a Solution


So the second therm in the SE tensor is symmetric so we need to prove that the first term is, too. But I am really not sure how to proceed for a general Lagrangian. For example, if we have a term like ##(\partial_\mu \phi)^2\partial_\nu \phi##, that wouldn't by symmetric. Am I reading this the wrong way? Thank you!
 

Answers and Replies

  • #2
Orodruin
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Your proposed Lagrangian term is not even Lorentz invariant ...
 
  • #3
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Your proposed Lagrangian term is not even Lorentz invariant ...
Oh sorry for that, I didn't mean that term is alone, it was just an example. It could be ##(\partial_\mu \phi)^2\partial_\nu \phi J^\nu## where I have an external source. My point was, what terms am I allowed to use (respecting Lorentz invariance) in the general case? I just don't know where to start from in solving this...
 

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