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   We study the theory of the (1/2,0)+(0,1/2) and (1,0)+(0,1) representations 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 behaviour of the helicity eigenstates with respect to the charge
conjugation, CP- conjugation is also different comparing with the parity
eigenstates.

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The categories of this paper are: math
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
9
The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org