What does Weinberg–Witten theorem want to express?

  • #1
Weinberg-Witten theorem states that massless particles (either composite or elementary) with spin ##j > 1/2## cannot carry a Lorentz-covariant current, while massless particles with spin ##j > 1## cannot carry a Lorentz-covariant stress-energy. The theorem is usually interpreted to mean that the graviton (##j = 2##) cannot be a composite particle in a relativistic quantum field theory.

While the argument is so strong and weird, how is it possible? Why can we not construct a theory which is massless charged vector field and therefore carry a Lorentz-covariant current ? And although we assume the second argument is right, which says massless particles with spin ##j > 1## cannot carry a Lorentz-covariant stress-energy, how does it imply that the graviton (##j = 2##) cannot be a composite particle ?
 

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  • #2
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Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
 
  • #3
atyy
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The Weinberg-Witten theorem implies that the graviton is not composite, because quantum fields usually have Lorentz-covariant stress-energy, and composite particles made from such fields will also have Lorentz-covariant stress-energy.

There is an interesting note in the Weinberg-Witten paper that the theorem does not exclude emergent gravity approaches like Sakharov's, because there the emergence is from quantum corrections, and not from composite particles.
 
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