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Open AccessArticle

Lorentz Group Projector Technique for Decomposing Reducible Representations and Applications to High Spins

Instituto de Física, Universidad Autońoma de San Luis Potosí, Av. Manuel Nava 6, Zona Universitaria, San Luis Potosí 78290, Mexico
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These authors contributed equally to this work.
Universe 2019, 5(8), 184; https://doi.org/10.3390/universe5080184
Received: 24 June 2019 / Revised: 25 July 2019 / Accepted: 1 August 2019 / Published: 7 August 2019
(This article belongs to the Special Issue Lorentz-Breaking Field Theory)
The momentum-independent Casimir operators of the homogeneous spin-Lorentz group are employed in the construction of covariant projector operators, which can decompose anyone of its reducible finite-dimensional representation spaces into irreducible components. One of the benefits from such operators is that any one of the finite-dimensional carrier spaces of the Lorentz group representations can be equipped with Lorentz vector indices because any such space can be embedded in a Lorentz tensor of a properly-designed rank and then be unambiguously found by a projector. In particular, all the carrier spaces of the single-spin-valued Lorentz group representations, which so far have been described as 2 ( 2 j + 1 ) column vectors, can now be described in terms of Lorentz tensors for bosons or Lorentz tensors with the Dirac spinor component, for fermions. This approach facilitates the construct of covariant interactions of high spins with external fields in so far as they can be obtained by simple contractions of the relevant S O ( 1 , 3 ) indices. Examples of Lorentz group projector operators for spins varying from 1 / 2 –2 and belonging to distinct product spaces are explicitly worked out. The decomposition of multiple-spin-valued product spaces into irreducible sectors suggests that not only the highest spin, but all the spins contained in an irreducible carrier space could correspond to physical degrees of freedom. View Full-Text
Keywords: homogenous Lorentz group; high spins; covariant projectors; decomposition of tensor products homogenous Lorentz group; high spins; covariant projectors; decomposition of tensor products
MDPI and ACS Style

Banda Guzmán, V.M.; Kirchbach, M. Lorentz Group Projector Technique for Decomposing Reducible Representations and Applications to High Spins. Universe 2019, 5, 184.

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