Peccei–Quinn theory

The Peccei-Quinn theory is a theoretical framework proposed to address the strong CP (Charge-Parity) problem in quantum chromodynamics (QCD), which is the fundamental theory of the strong interaction between quarks and gluons. Formulated in 1977 by Roberto Peccei and Helen Quinn, the theory introduces a new class of particles called axions, which are proposed as a solution to this problem.