Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electric Dipole Moment from QCD $\theta$ and How It Vanishes for Mixed
  States   In a previous paper [1], we studied the $\eta'$ mass and formulated its
chirally symmetric coupling to fermions which induces electric dipole moment
(EDM). Here we calculate the EDM to one-loop. It is finite, having no
ultraviolet divergence while its infrared divergence is canceled by soft photon
emission processes \emph{exactly} as for $\theta=0$. The coupling does not lead
to new divergences (not present for $\sin\theta=0$) in soft photon processes
either. Furthermore, as it was argued previously [1], the EDM vanishes if
suitable mixed quantum states are used. This means that in a quantum theory
based on such mixed states, a strong bound on EDM will not necessarily lead to
a strong bound such as $|\sin \theta|\lesssim 10^{-11}$ . This fact eliminates
the need to fine-tune $\theta$ or for the axion field.

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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: stat
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The categories of this paper are: hep-lat
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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: mtrl-th
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The categories of this paper are: q-fin
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The categories of this paper are: chem-ph
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The categories of this paper are: econ
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The categories of this paper are: q-bio
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The categories of this paper are: supr-con
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The categories of this paper are: astro-ph
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg