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Strong CP problem

The strong CP problem is a question in particle physics, which brings up the following quandary: why does quantum chromodynamics (QCD) seem to preserve CP-symmetry?

In particle physics, CP stands for the combination of C-symmetry (charge conjugation symmetry) and P-symmetry (parity symmetry). According to the current mathematical formulation of quantum chromodynamics, a violation of CP-symmetry in strong interactions could occur. However, no violation of the CP-symmetry has ever been seen in any experiment involving only the strong interaction. As there is no known reason in QCD for it to necessarily be conserved, this is a "fine tuning" problem known as the strong CP problem.

The strong CP problem is sometimes regarded as an unsolved problem in physics, and has been referred to as "the most underrated puzzle in all of physics."[1][2] There are several proposed solutions to solve the strong CP problem. The most well-known is Peccei–Quinn theory,[3] involving new pseudoscalar particles called axions.

  1. ^ Mannel, T. (2–8 July 2006). "Theory and Phenomenology of CP Violation" (PDF). Nuclear Physics B. The 7th International Conference on Hyperons, Charm, and Beauty Hadrons (BEACH 2006). Vol. 167. Lancaster: Elsevier. pp. 170–174. Bibcode:2007NuPhS.167..170M. doi:10.1016/j.nuclphysbps.2006.12.083. Retrieved 15 Aug 2015.
  2. ^ "The 'Strong CP Problem' is the Most Underrated Puzzle in All of Physics". Forbes.
  3. ^ Peccei, R.D.; Quinn, H.R. (1977). "CP conservation in the presence of pseudoparticles". Physical Review Letters. 38 (25): 1440–1443. Bibcode:1977PhRvL..38.1440P. doi:10.1103/PhysRevLett.38.1440.

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