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Origin of the matter-antimatter asymmetry

The Big Bang should have made equal amounts of matter and antimatter, yet the universe contains almost only matter. The SM cannot produce the observed excess.

Why it matters

The existence of matter requires physics beyond the SM, of a kind that may be testable.

Review

D. Bodeker, W. Buchmuller, Baryogenesis from the weak scale to the grand unification scale, Reviews of Modern Physics, 2021. https://arxiv.org/abs/2009.07294 reference checked

Timestamp record

Signed record: c54812d3b8f0…
Public log: Entry 238, in checkpoint 2,123
In the log by: Block 969,698, 2026-10-03

This text was in the PubPhys log by that date. The date says nothing about when the problem was first posed.

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3 problems

Which mechanism produced the cosmic baryon asymmetry?

Open

For every billion antiquarks there were about a billion and one quarks in the early universe. Something broke the matter-antimatter balance, and we do not know what.

Can electroweak baryogenesis survive the electron EDM bound?

Open

The asymmetry could have formed when the Higgs field switched on, but that needs new CP-violating forces near the weak scale. Such forces would also give the electron a tiny electric dipole, which has not been seen.

Do GeV-scale heavy neutral leptons realize low-scale leptogenesis?

Open

In one scenario, heavy partners of neutrinos with masses near a few proton masses created the asymmetry. Such particles could be made at accelerators and seen decaying.