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--- models:speculative_models:axion [2018/04/08 17:25]
georgefarr ↷ Links adapted because of a move operation
+++ models:speculative_models:axion [2019/07/01 09:24]
jakobadmin [Criticism]
@@ Line 31: / Line 31: @@
 <tabbox Concrete>
+  * A really great and short introduction is [[https://www.sciencedirect.com/science/article/pii/S1631070511002039|The strong CP problem by Pierre Sikivie]]
   * [[https://arxiv.org/abs/1712.03018|Axions and ALPs: a very short introduction]] by David J. E. Marsh
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 <cite>[[https://arxiv.org/pdf/1608.08969.pdf|Domestic Axion]] Gia Dvali</cite>
 </blockquote>
+<blockquote>The notion of Peccei–Quinn (PQ) symmetry may seem contrived. Why should there be a U(1) symmetry which is broken at the quantum level but which is exact at the classical level? However, the reason for PQ symmetry may be deeper than we know at present. String theory contains many examples of symmetries which are exact classically but which are broken by quantum anomalies, including PQ symmetry [17–19]. Within field theory, there are examples of theories with automatic PQ symmetry, i.e. where PQ symmetry is a consequence of just the particle content of the theory without adjustment of parameters to special values. <cite>[[https://www.sciencedirect.com/science/article/pii/S1631070511002039|The strong CP problem by Pierre Sikivie]]</cite></blockquote>
 </tabbox>