Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Newton-Wigner position operator and its corresponding spin operator in
  relativistic quantum mechanics   A relativistic spin operator is to be the difference between the total and
orbital angular momentum. As the unique position operator for a localized
state, the remarkable Newton-Wigner position operator, which has all desirable
commutation relations as a position operator, can give a proper spin operator.
Historically important three spin operators respectively proposed by Bogolubov
et al., Pryce, and Foldy-Woutheysen are investigated to manifest a
corresponding spin operator to the Newton-Wigner position operator. We clarify
a unique spin operator in relativistic quantum mechanics described by the Dirac
Hamiltonian.

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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cs
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: stat