Is the Energy Momentum Tensor for Scalar Fields Always Symmetric?

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The discussion centers on proving that the energy momentum tensor for scalar fields is symmetric, specifically that Tμν = Tνμ when the Lagrangian depends solely on scalar fields φ. The equation for the energy momentum tensor is provided, and the challenge lies in demonstrating the symmetry of the first term, given that the second term is inherently symmetric. A participant expresses confusion about how to approach the proof for a general Lagrangian, particularly when considering terms like (∂μφ)²∂νφ, which may not be symmetric. The conversation highlights the need for Lorentz invariant terms in the Lagrangian to ensure the validity of the proof. Overall, the thread emphasizes the complexities involved in establishing the symmetry of the energy momentum tensor in scalar field theories.
BillKet
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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!
 
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Your proposed Lagrangian term is not even Lorentz invariant ...
 
Orodruin said:
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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