Derivation of the θ-parameter in Quantum Chromodynamics

Abstract

An ongoing challenge of the Standard Model is to explain the nearly vanishing magnitude of CP symmetry breaking in Quantum Chromodynamics (QCD). This challenge goes by the name of the strong CP problem and is quantified by the θ-parameter of the QCD Lagrangian. It is known that axions are hypothetical particles conjectured to offset the contribution of the θ-parameter and restore the CP symmetry of QCD. Starting from the near equilibrium interpretation of gluon dynamics, here we bypass the axion conjecture and derive the numerical value of the θ-parameter in close agreement with experimental bounds. A surprising finding of this brief report is that the strong CP and the baryon asymmetry problems appear to be related to each other.