Is the Energy Momentum Tensor for Scalar Fields Always Symmetric?

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SUMMARY

The discussion centers on the symmetry of the energy momentum tensor for scalar fields, specifically demonstrating that if the Lagrangian depends solely on scalar fields, the tensor is symmetric: ##T_{\mu\nu}=T_{\nu\mu}##. The energy momentum tensor is defined as ##T_{\mu\nu}=\frac{\partial L}{\partial(\partial_\mu\phi)}\partial_\nu\phi-g_{\mu\nu}L##. The participants debate the implications of specific Lagrangian terms, particularly the need for Lorentz invariance in constructing valid terms for the tensor.

PREREQUISITES
  • Understanding of Lagrangian mechanics and field theory
  • Familiarity with the energy momentum tensor and its derivation
  • Knowledge of Lorentz invariance in physics
  • Basic concepts of scalar fields in theoretical physics
NEXT STEPS
  • Research the derivation of the energy momentum tensor for various field types
  • Study Lorentz invariance and its implications for Lagrangian formulations
  • Explore examples of scalar field Lagrangians and their corresponding energy momentum tensors
  • Investigate the role of external sources in modifying the energy momentum tensor
USEFUL FOR

The discussion is beneficial for theoretical physicists, graduate students in physics, and anyone studying field theory and the properties of scalar fields.

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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