Explain the origin of the Universe’s matter–antimatter asymmetry

Develop a successful mechanism for the creation of primordial protons, neutrons, and electrons—baryogenesis and leptogenesis—that accounts for the observed surplus of matter over antimatter in the Universe.

Background

The paper reviews Sakharov’s conditions (baryon number violation, C and CP violation, and departure from thermal equilibrium) and notes that, within the Standard Model, these effects are insufficient by several orders of magnitude to generate the observed baryon asymmetry.

Thus, identifying a viable baryogenesis/leptogenesis mechanism remains an outstanding challenge in particle physics and cosmology.

References

Consequently, the creation of primordial protons, neutrons and electrons (baryogenesis and leptogenesis), remains one of the most challenging problems in particle physics at the present time.

— Antimatter  (2412.12128 - Gato-Rivera, 2024) in Section 6. Matter–antimatter asymmetry

Whether the required large asymmetries may be generated within particular realistic models of sterile neutrino dark matter, like e.g. $\nu$MSM , remains an open question to be further investigated.

— Natural Saturation Of The Sterile Neutrino Dark Matter Resonant Production By a High Lepton Flavor Asymmetry In Primordial Plasma  (2609.31340 - Gorbunov et al., 25 Sep 2026) in Conclusion

A more detailed construction of a concrete cosmological scenario realizing both the heavy-Higgsino dark-matter abundance and successful baryogenesis is left for future work.

— From the LZ Event to Grand Unification: Heavy Higgsinos and Proton Decay  (2610.01613 - Hor et al., 1 Oct 2026) in Section 3.1, “Cosmology”