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arXiv · hep-ph/0607268

The Strong CP Problem and Axions

R. D. Peccei
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Abstract

I describe how the QCD vacuum structure, necessary to resolve the $U(1)_A$ problem, predicts the presence of a P, T and CP violating term proportional to the vacuum angle $\barθ$. To agree with experimental bounds, however, this parameter must be very small $(\barθ \leq 10^{-9}$). After briefly discussing some possible other solutions to this, so-called, strong CP problem, I concentrate on the chiral solution proposed by Peccei and Quinn which has associated with it a light pseudoscalar particle, the axion. I discuss in detail the properties and dynamics of axions, focusing particularly on invisible axion models where axions are very light, very weakly coupled and very long-lived. Astrophysical and cosmological bounds on invisible axions are also briefly touched upon.

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R. D. Peccei. 2006-07-24. The Strong CP Problem and Axions. https://doi.org/10.1007/978-3-540-73518-2_1

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