Commutator notation in classical field theory

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Homework Help Overview

The discussion revolves around the notation used in classical field theory, specifically the term \(\partial_{[ \mu}F_{\nu \rho ]}\) in the context of Maxwell's equations and the field strength tensor \(F^{\mu \nu}\). Participants are exploring the meaning and implications of this notation.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the notation and its definition, questioning whether it involves permuting the indices. Other participants provide insights into the antisymmetrizing operation and its relation to differential forms.

Discussion Status

Participants are actively engaging with the notation, with some offering references to lecture notes and resources that may clarify the concept. There is a recognition of the need for further understanding, particularly for those less familiar with the underlying principles of general relativity and differential geometry.

Contextual Notes

One participant mentions their lack of background in general relativity, indicating that the discussion may be influenced by varying levels of familiarity with the subject matter.

paco_uk
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Homework Statement



Could someone please explain what is meant by the term:

[itex]\partial_{[ \mu}F_{\nu \rho ]}[/itex]

Homework Equations



I have come across this in the context of Maxwells equations where [tex]F^{\mu \nu}[/tex] is the field strength tensor and apparently:

[tex]\partial_{[ \mu}F_{\nu \rho ]} =0[/tex]

follows "trivially" from

[tex]F_{\mu \nu} = \partial_{\mu} A_{\nu} - \partial_{\nu} A_{\mu}[/tex]



The Attempt at a Solution



I don't understand what the notation means and I haven't found it defined anywhere. Do all three indices get permuted somehow?
 
Last edited:
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Would you please fix your latex tags?
They should be [ tex ]...[ /tex ] (that is: forward slash, but no spaces within the tag).

You'll see that your equation will look "strange" then.
Could you perhaps fix that as well?
 
Sorry about the mess. I've cleared up the latex tags. What's there now does indeed look strange to me but is what is written in the lecture notes. I don't know what the commutator bracket round the subscripts means.
 
paco_uk said:
I don't understand what the notation means and I haven't found it defined anywhere. Do all three indices get permuted somehow?

Yes. This is the antisymmetrizing operation. A good explanation is given in Prof. Maloney's notes and lecture recordings. It's also found in many good reference books on GR and differential geometry.

http://www.physics.mcgill.ca/~maloney/514/

Here is a PDF of the relevant lecture notes, but it's helpful to listen to the lectures if you have time.
 

Attachments

The notation makes sense, if you learn about differential forms on the space-time manifold. The F is then a 2-form, and dF =0 is a consequence of the 2-nd degree nilpotency of the exterior differential.
 
Thanks very much. I've never done a course on General Relativity so I'm pretty shaky on all this. I look forward to listening to the lectures.
 

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