Strong CP problem: Difference between revisions

Revision as of 15:58, 8 February 2020

Revision as of 19:31, 3 May 2020

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The strong CP problem is sometimes regarded as an [[List of unsolved problems in physics|unsolved problem in physics]], and has been referred to as "the most underrated puzzle in all of physics."<ref>{{cite conference |first=Thomas |last=Mannel |title=Theory and Phenomenology of CP Violation |booktitle=Nuclear Physics B

|volume=167 |pages=170–174 |publisher=Elsevier |conference=The 7th International Conference on Hyperons, Charm, and Beauty Hadrons (BEACH 2006) |date=2–8 July 2006 |___location=Lancaster |url=https://indico.cern.ch/event/427023/session/6/contribution/43/attachments/912026/1288208/Lancester-Mannel-Proc.pdf |doi=10.1016/j.nuclphysbps.2006.12.083 |accessdate=15 Aug 2015 |bibcode=2007NuPhS.167..170M}}</ref><ref>{{Cite web | url=https://www.forbes.com/sites/startswithabang/2019/11/19/the-strong-cp-problem-is-the-most-underrated-puzzle-in-all-of-physics |title = The 'Strong CP Problem' is the Most Underrated Puzzle in All of Physics}}</ref> There are several proposed solutions to solve the strong CP problem. The most well-known is [[Peccei–Quinn theory]],<ref>{{Cite journal|last1=Peccei|first1=Roberto D.|last2=Quinn|first2=Helen R.|authorlink2=Helen Quinn|year=1977|title=''CP'' conservation in the presence of pseudoparticles|url=https://www.researchgate.net/publication/248549883|journal=[[Physical Review Letters]]|volume=38|issue=25|pages=1440–1443|bibcode=1977PhRvL..38.1440P|doi=10.1103/PhysRevLett.38.1440|authorlink1=Roberto Peccei}}</ref> involving new [[pseudoscalar]] particles called [[axion]]s.

==CP violation==

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If at least one of the [[quarks]] of the standard model were massless, ''{{mvar|θ}}'' would become unobservable; i.e. it would vanish from the theory. However, empirical evidence strongly suggests that none of the quarks are massless and so this solution to the strong CP problem fails.

==Proposed solutions==

There are several proposed solutions to solve the strong CP problem. The most well-known is [[Peccei–Quinn theory]],<ref>{{Cite journal |last1=Peccei |first1=Roberto D. |authorlink1=Roberto Peccei |last2=Quinn |first2=Helen R. |authorlink2=Helen Quinn |year=1977 |title=''CP'' conservation in the presence of pseudoparticles |journal=[[Physical Review Letters]] |volume=38 |issue=25 |pages=1440–1443 |doi=10.1103/PhysRevLett.38.1440 |bibcode=1977PhRvL..38.1440P |url=https://www.researchgate.net/publication/248549883}}</ref> involving new [[pseudoscalar]] particles called [[axion]]s.

==See also==