Let the helicity operator be $\frac{P \cdot J}{P^0}$ with an eigenvalue $\lambda$. Then why do renormalizable theories have $|\lambda| \le 1?$ (in general dimensions or in 4ds?)

Also, what is the kinetic term of a spin-s particle? For example, for spin-2 particle.

  • $\begingroup$ @G.Smith in p.31 of arXiv:1011.1491v1 $\endgroup$ – Liberty Mar 27 at 5:07
  • $\begingroup$ Your second question should be posted separately. We have a one-question-per-post rule on this site. Thanks. $\endgroup$ – G. Smith Mar 27 at 5:08
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    $\begingroup$ @G.Smith i guess the second question is related to the first question by counting the engineering dimensions of the kinetic term. $\endgroup$ – Liberty Mar 27 at 5:09

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