Abstract.We study the Weyl algebra A pertaining to a particle constrained on a sphere, which is generated by the coordinates n and by the angular momentum J . A is the algebra E3 of the Euclidean group in space. We find its irreducible representations by a novel approach, by showing that they are the irreducible representations (l0, 0) of so(3, 1) , with l0 or -l0 being equal to the Casimir operator J.n . Any integer or half-integer l0 is allowed. The Hilbert space of a particle of spin S hosts 2S + 1 such representations. J can be analyzed into the sum L + S , i.e. pure spin states can be identified, provided 2S + 1 irreducible representations of A are glued together. These results apply to any surface which is diffeomorphic to S2.
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