Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Helicity Basis for Spin 1/2 and 1, and Discrete Symmetry Operations   We study the theory of the (1/2,0)+(0,1/2) and (1,0)+(0,1) representations of
the Lorentz group in the helicity basis. The helicity eigenstates are not the
parity eigenstates. This is in accordance with the idea of Berestetskii,
Lifshitz and Pitaevskii. The properties of the helicity eigenstates with
respect to the charge conjugation and the CP- conjugation are also considered.

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The categories of this paper are: ao-sci
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The categories of this paper are: atom-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: acc-phys
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: mtrl-th