The Baryon Asymmetry Problem: A Review of Theories and Controversies

The issue of baryon asymmetry, or matter–antimatter inequality, is one of the largest open issues in cosmology and particle physics. Experiments indicate that the universe is dominated by matter, with a lot fewer antimatter, although the Big Bang had produced them in equal proportions. Overcoming this disparity is critical, as it is the cause behind the presence of galaxies, stars, planets, and life is embedded in this inequality. This is a review of today’s best theories, electroweak baryogenesis, leptogenesis, and Grand Unified Theory (GUT) baryogenesis—judging their mechanisms, merits, and demerits. Cosmological evidence from the cosmic microwave background, Big Bang nucleosynthesis, and recent CP violation measurements in baryons provides significant constraints on these theories. The article also discusses the issues and disagreements in baryogenesis, such as insufficient Standard Model CP violation, theory uncertainties, and experimental inadequacies.