Of course, there are acceptable theories that have massless charged particles with spin
(such as the massless version of the original Yang–Mills theory), and also
theories that have massless particles with spin
(such as supersymmetry theories
or general relativity). Our theorem does not apply to these theories because they do not
have Lorentz-covariant conserved currents or energy-momentum tensors, respectively.
Furthermore, when it comes to Sakharov-style induced gravity those authors explicitly state [673]:
However, the theorem dearly does not apply to theories in which the gravitational field is a basic degree of freedom but the Einstein action is induced by quantum effects.
That is: The Weinberg–Witten theorem has no direct application to analogue spacetimes – at the kinematic
level it has nothing to say, at the dynamic level its applicability is rather limited by the stringent
technical assumptions invoked – specifically exact Lorentz invariance at all scales – and the
fact that these technical assumptions are not applicable in the current context. For careful
discussions of the technical assumptions see [596, 366, 212, 404]. Note particularly the comment by
Kubo [366]
… the powerful second part of the theorem becomes empty in the presence of gravity …
Finally we mention that, though motivated by quite different concerns, the review article [61] gives a good overview of the Weinberg–Witten theorem, and the ways in which it may be evaded.
http://www.livingreviews.org/lrr-2011-3 |
Living Rev. Relativity 14, (2011), 3
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