Spontaneous baryogenesis from axions with generic couplings

Abstract

Axion-like particles can source the baryon asymmetry of our Universe through spontaneous baryogenesis. Here we clarify that this is a generic outcome for essentially any coupling of an axion-like particle to the Standard Model, requiring only a non-zero velocity of the classical axion field while baryon or lepton number violating interactions are present in thermal bath. In particular, coupling the axions only to gluons is sufficient to generate a baryon asymmetry in the presence of electroweak sphalerons or the Weinberg operator. Deriving the transport equation for an arbitrary set of couplings of the axion-like particle, we provide a general framework in which these results can be obtained immediately. If all the operators involved are efficient, it suffices to solve an algebraic equation to obtain the final asymmetries. Otherwise one needs to solve a simple set of differential equations. This formalism clarifies some theoretical subtleties such as redundancies in the axion coupling to the Standard Model particles associated with a field rotation. We demonstrate how our formalism automatically evades potential pitfalls in the calculation of the final baryon asymmetry.

Predictions for axion couplings from ALP cogenesis

“…Note added. While finalizing the manuscript, ref [81]. appeared on arXiv, which also discusses the baryon asymmetry from general couplings of the ALP with Standard Model particles, and derives the dependence of the baryon asymmetry on the couplings.…”

Lepto-axiogenesis

“…Note added. While finalizing our manuscript, an interesting paper appeared on the arXiv [160]. This has an overlap with our paper as it discusses the production of B − L asymmetry from a non-zero velocity of a generic axion field and the dimension-five interaction.…”

Spontaneous leptogenesis in Higgs inflation

“…Therefore once the lepton (or baryon) number is generated by certain processes in the early universe, the chemical potential will contribute to the generation of net lepton (or baryon) number. We note that similar derivative couplings (or variations) have been adopted to explain baryon asymmetry in earlier works [14][15][16].…”

“…The spin connection in the Jordan frame ω Jabµ is related to the spin connection ω Jab and vielbein e aµ in the Einstein frame ω Jabµ = ω abµ + e bµ ∂ a ln Ω − e aµ ∂ b ln Ω (A. 15) and this results in…”

“…The first equation of eq. (B.8) for u and v can be rearranged to Note that the terms in the second line exactly cancelled as 15) and the similar procedure can be applied to the second equation of eq. (B.8).…”