Leptogenesis

Leptogenesis is a proposed early-universe mechanism that creates an excess of leptons over antileptons, which electroweak sphaleron processes partly convert into the observed excess of matter over antimatter.

Heavy neutral lepton: A neutral fermion heavier than the known neutrinos, often introduced to generate neutrino masses. In many models, its out-of-equilibrium decays create the initial lepton asymmetry.
Baryon asymmetry: The observed excess of baryons over antibaryons in the universe. Leptogenesis aims to explain this matter–antimatter imbalance indirectly.
Mikhail Shaposhnikov: A theoretical physicist known for work on particle physics, cosmology, and the origin of matter. His 1980s work helped develop the connection between lepton asymmetry and baryon asymmetry.
Electroweak baryogenesis: A mechanism that generates baryon asymmetry during the electroweak phase transition. It creates the asymmetry near the electroweak scale rather than first generating lepton number.
Neutrino oscillation: The quantum-mechanical transformation of one neutrino flavor into another during propagation. Measured neutrino mixing constrains models, but does not by itself establish the high-energy CP violation needed.
CP violation: A difference between the behavior of particles and antiparticles under charge conjugation and parity reversal. Unequal decay rates into leptons and antileptons require CP violation.
Lepton number: A quantum number that assigns positive values to leptons and negative values to antileptons. Generating a lepton asymmetry means producing a nonzero net lepton number or flavored equivalent.
Mikhail Fukugita: A Japanese theoretical physicist who co-developed the modern thermal leptogenesis scenario. His 1986 work with Yanagida established a prominent heavy-neutrino decay mechanism.
Affleck–Dine baryogenesis: A baryogenesis mechanism in supersymmetric theories driven by coherent scalar-field motion. It generates asymmetry through scalar condensates instead of heavy-neutrino decays.
Neutrino mass ordering: The unresolved question of whether the third neutrino mass eigenstate is heaviest or lightest. The ordering can sharpen constraints connecting low-energy neutrino data to leptogenesis models.

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