Yes, a small violation of the charge-parity (CP) symmetry in the strong interaction, known as CP violation in quantum chromodynamics (QCD), is one of the potential explanations for the observed matter-antimatter asymmetry in the universe. However, it is important to note that this explanation alone is not sufficient to fully account for the matter-antimatter asymmetry, and other mechanisms are also believed to contribute to the phenomenon.
CP violation refers to the violation of the combined symmetry of charge conjugation (C) and parity (P). In the context of the strong interaction described by QCD, CP violation can occur due to the complex nature of the quark mixing matrix, which governs the interactions between different types of quarks. This mixing matrix, known as the Cabibbo-Kobayashi-Maskawa (CKM) matrix, contains complex phases that can lead to CP violation.
While CP violation in the CKM matrix has been observed in experiments involving weak interactions, it is not sufficient to explain the observed matter-antimatter asymmetry in the universe. This is because the amount of CP violation in the CKM matrix is not large enough to generate the observed baryon asymmetry.
Therefore, additional sources of CP violation beyond the CKM matrix, such as new physics beyond the Standard Model, may be required to explain the matter-antimatter asymmetry. One such possibility is the existence of new particles or interactions, such as those predicted by theories like supersymmetry or models with extra dimensions. These extensions to the Standard Model could introduce additional sources of CP violation that could contribute to the generation of the matter-antimatter asymmetry.
Another proposed mechanism to explain the matter-antimatter asymmetry is through the hypothetical particle called the axion, which you mentioned in your question. While the axion was originally proposed to solve the strong CP problem in QCD, its existence could also have implications for the matter-antimatter asymmetry. However, no direct experimental evidence for the axion has been found.
In summary, while CP violation in QCD can contribute to the matter-antimatter asymmetry, additional sources of CP violation and mechanisms beyond the Standard Model may be required to fully explain this fundamental puzzle of the universe.