# What does Weinberg–Witten theorem want to express?

1. Dec 18, 2014

### Ganesh Ujwal

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 ?

2. Dec 23, 2014