The Weinberg-Witten theorem (https://en.wikipedia.org/wiki/Weinberg–Witten_theorem) states that(adsbygoogle = window.adsbygoogle || []).push({});

A ##3 + 1##D QFT quantum field theory with a conserved ##4##-vector current ##J^\mu## which is Poincaré covariant does not admit massless particles with helicity ##|h| > 1/2##.

A ##3 + 1##D QFT with a conserved stress–energy tensor ##T^{\mu \nu}## which is Poincaré covariant does not admit massless particles with helicity ##|h| > 1##.

This theorem is interpreted to mean that the graviton cannot be a composite particle. However, I do not quite follow this interpretation.

My understanding is that the massless graviton of spin ##2##ought to havea Poincare-covariant conserved stress-tensor (and Poincare-covariant conserved ##4##-vector currents associated to other symmetries). So the Weinberg-Witten theorem means the gravitonis not allowed to exist at all.

That the graviton is not allowed to be a composite particle appears to be a weaker conclusion.

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# A Interpretation of the Weinberg-Witten theorem

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