The Weinberg-Witten theorem on massless particles: an essay

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In this essay we deal with the Weinberg-Witten theorem [1] which imposes limitations on massless particles. First we motivate a classification of massless particles given by the Poincar´e group as the symmetry group of Minkowski spacetime. We then use the fundamental structure of the background in the form of Poincar´e covariance to derive restrictions on charged massless particles known as the Weinberg-Witten theorem. We address possible misunderstandings in the proof of this theorem motivated by several papers on this topic. In the last section the consequences of the theorem are discussed. We treat it in the context of known particles and as a constraint for emergent theories.