Strong CP problem

Strong CP problem: why does QCD not violate CP symmetry?

Quantum chromodynamics (QCD) theoretically allows for CP-symmetry violation in strong interactions, yet experiments show no such violation.

The strong CP problem arises because QCD does not have a known reason to conserve CP-symmetry, leading to a fine-tuning issue in particle physics.

Several solutions, including the Peccei–Quinn theory with axions, have been proposed to address this unsolved puzzle.

Example

No experimental evidence of CP-symmetry violation in strong interactions despite QCD's theoretical allowance.

Understanding the strong CP problem is crucial for advancing theoretical physics and achieving a unified understanding of fundamental forces.

Related concepts

CP violation

CP violation discovered in 1964 neutral kaon decays

CPT symmetry

CPT symmetry is conserved in all physical phenomena

QCD (quantum chromodynamics) describes

QCD describes the strong force between quarks mediated by gluons

Asymptotic safety

Quarks interact more weakly at higher energies, earning the 2004 Nobel Prize

Goldstone boson

Goldstone theorem states every spontaneously broken continuous symmetry produces a massless boson

Spontaneous symmetry breaking

Spontaneous symmetry breaking occurs even when laws retain symmetry

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