Axiogenesis: Rotating Axions & Baryon Asymmetry

• Axiogenesis is a baryogenesis mechanism where a rotating QCD axion field generates a conserved Peccei–Quinn charge that sphalerons convert into baryon asymmetry.
• It leverages explicit PQ breaking and anomalous charge transport to resolve tensions such as dark matter overproduction and axion quality issues.
• Variants like lepto-axiogenesis, R-parity-violating, and SU(2)_R-assisted models illustrate its adaptability to constraints from electroweak freeze-out and gravitational wave signals.

Searching arXiv for relevant papers on axiogenesis and related subtopics. Axiogenesis is a class of mechanisms in which an early-Universe axion, usually the QCD axion, rotates in field space and the associated Peccei–Quinn (PQ) charge is converted into the observed baryon asymmetry through anomalous charge transport and sphaleron dynamics. In its original formulation, a PQ-charged scalar is spun up by explicit PQ breaking in the early Universe, and the resulting PQ asymmetry is converted into a baryon asymmetry via QCD and electroweak sphaleron transitions (Co et al., 2019). The term has since expanded to include lepto-axiogenesis, $R$-parity-violating and $SU(2)_R$-assisted variants, heavy-axion and multi-axion realizations, and several proposals for resolving the associated dark-matter and axion-quality tensions (Barnes et al., 2022). A separate, unrelated usage also appears in developmental biophysics, where “axiogenesis” refers to mechanisms of axon growth regulation (Folz et al., 2018).

1. Foundational mechanism and dynamical variables

The central dynamical variable in the cosmological literature is the axion angle,

$\theta \equiv \frac{a}{f_a},$

whose rotation carries a conserved PQ charge density

$n_\theta = \dot\theta\, f_a^2.$

In this language, axiogenesis is a spontaneous-baryogenesis-like mechanism in which $\dot\theta$ acts as the source term for anomalous fermion-number production while the coherent axion rotation stores the charge reservoir (Co et al., 13 Nov 2025). The observed baryon asymmetry to be reproduced is

$Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$

a value used repeatedly as the normalization target in the literature (Co et al., 2019).

The original construction assumes that the PQ symmetry is explicitly broken in the early Universe, so that the PQ field is torqued into rotation and acquires a nonzero charge asymmetry. Once the explicit breaking becomes negligible, the charge stored in the rotation is approximately conserved and can be redistributed to thermal plasma asymmetries by anomalous processes (Co et al., 2019). This makes the rotating axion condensate analogous to an Affleck–Dine condensate, but with PQ charge rather than baryon or lepton number as the primary stored quantity.

Axiogenesis is therefore not merely “baryogenesis with an axion present.” Its defining feature is that the axion’s coherent angular momentum in field space is the origin of the asymmetry budget. This distinguishes it from ordinary misalignment cosmology, from conventional thermal leptogenesis, and from electroweak baryogenesis driven by phase-transition CP violation.

2. Charge transfer, sphalerons, and lepton-violating variants

In minimal axiogenesis, the rotating QCD axion biases anomalous charge transport, and the baryon yield is commonly written as

$$Y_B = c_B \frac{T_{\rm EW}^2}{f_a^2} Y_\theta, \qquad Y_\theta \equiv \frac{n_\theta}{s},$$

with $T_{\rm EW}\simeq 130\ {\rm GeV}$ the electroweak sphaleron decoupling temperature and $c_B$ a transport coefficient (Co et al., 13 Nov 2025). In this picture, strong sphalerons first transfer the PQ asymmetry into quark chiral asymmetries, and electroweak sphalerons then convert these into baryon number, freezing in the final result when weak sphalerons switch off (Madge et al., 2021).

A large part of the subsequent literature replaces direct $B+L$ conversion by a more efficient $SU(2)_R$0-violating channel. In lepto-axiogenesis, the relevant interaction is the Weinberg operator $SU(2)_R$1, or, in explicit neutrino models, the dynamics of right-handed neutrinos. The baryon asymmetry then arises from a lepton asymmetry which electroweak sphalerons partially convert according to

$SU(2)_R$2

This class of models is technically distinct from minimal axiogenesis because the axion-induced chemical potential is read out through lepton-number violation rather than by weak sphalerons alone (Barnes et al., 2022).

Once light or intermediate-mass right-handed neutrinos are treated explicitly rather than integrated out, two regimes emerge: an equilibrium freeze-out regime and a freeze-in regime. In the first, the relevant $SU(2)_R$3 interactions remain in equilibrium until $SU(2)_R$4 becomes nonrelativistic; in the second, the asymmetry never equilibrates and instead freezes in, with the produced $SU(2)_R$5 directly proportional to $SU(2)_R$6 (Barnes et al., 2024). This changes both the efficiency and the required saxion scale relative to high-scale lepto-axiogenesis.

A related extension uses $SU(2)_R$7-parity-violating couplings as the $SU(2)_R$8-violating sector. There, strong sphalerons transfer the axion’s angular momentum into a quark chiral asymmetry, and supersymmetric $SU(2)_R$9-parity violation converts that asymmetry into the baryon asymmetry (Co et al., 2021). Another replaces the standard electroweak freeze-out with an $\theta \equiv \frac{a}{f_a},$0 phase transition, so that baryogenesis is frozen in at the $\theta \equiv \frac{a}{f_a},$1 sphaleron decoupling temperature rather than at $\theta \equiv \frac{a}{f_a},$2 GeV (Harigaya et al., 2021).

3. Principal realizations in the literature

The literature now contains several structurally distinct forms of axiogenesis. The main variants differ less in the existence of axion rotation than in the channel that converts PQ charge into a conserved asymmetry, the thermal epoch at which freeze-out occurs, and the mechanism that prevents overproduction of axion relics.

Realization	Distinct ingredient	Representative paper
Minimal axiogenesis	QCD and electroweak sphaleron transfer	(Co et al., 2019)
Lepto-axiogenesis	Weinberg operator or explicit $\theta \equiv \frac{a}{f_a},$3 dynamics	(Barnes et al., 2022, Barnes et al., 2024)
$\theta \equiv \frac{a}{f_a},$4-parity-violation axiogenesis	SUSY $\theta \equiv \frac{a}{f_a},$5 violation from RPV couplings	(Co et al., 2021)
$\theta \equiv \frac{a}{f_a},$6 axiogenesis	Freeze-out at an $\theta \equiv \frac{a}{f_a},$7 phase transition	(Harigaya et al., 2021)
Heavy-QCD-axion axiogenesis	Heavy unstable axion avoids late overclosure	(Co et al., 2022)
Axiverse or dark-sector-dissipative variants	Extra axions or monopole/dark gauge dissipation	(Asadi et al., 19 Nov 2025, Co et al., 13 Nov 2025)

Minimal axiogenesis remains the conceptual baseline, but much of the later model building is driven by its tensions. Heavy-QCD-axion axiogenesis addresses those tensions by raising the axion mass to the MeV–GeV range while preserving the strong-CP solution; the viable region quoted is $\theta \equiv \frac{a}{f_a},$8 between $\theta \equiv \frac{a}{f_a},$9 and $n_\theta = \dot\theta\, f_a^2.$0 with $n_\theta = \dot\theta\, f_a^2.$1 (Co et al., 2022). The $n_\theta = \dot\theta\, f_a^2.$2 realization instead changes the baryon-violating sector, deriving

$n_\theta = \dot\theta\, f_a^2.$3

which directly correlates $n_\theta = \dot\theta\, f_a^2.$4 with the $n_\theta = \dot\theta\, f_a^2.$5 breaking scale and the $n_\theta = \dot\theta\, f_a^2.$6 mass (Harigaya et al., 2021).

A different branch of the subject merges axiogenesis with axion cogenesis. In the inflationary cogenesis scenario, the PQ field is driven to a Planckian value during inflation, the angular mode is made heavy by temporary explicit PQ breaking, and rotation begins immediately after inflation when the sign of the Hubble-induced mass flips. In that setup, lepto-axiogenesis is the more efficient baryogenesis channel and leads to the qualitative prediction $n_\theta = \dot\theta\, f_a^2.$7 in the viable QCD-axion region (Co et al., 2023).

4. Central tensions: dark matter, axion quality, and plasma backreaction

The defining technical tension of minimal axiogenesis is that the same $n_\theta = \dot\theta\, f_a^2.$8 needed to generate the observed baryon asymmetry tends to leave too much rotational energy in the axion sector. In the monopole-assisted analysis, the minimal scenario is described as overproducing axion dark matter by about a factor of $n_\theta = \dot\theta\, f_a^2.$9 (Co et al., 13 Nov 2025). In the axiverse analysis, the same conflict is summarized as underproducing baryons or overproducing dark matter by two to three orders of magnitude, depending on how the initial rotation is chosen (Asadi et al., 19 Nov 2025).

Several distinct resolutions have been proposed. One is to let the axion be heavy and unstable, so that the post-baryogenesis rotation does not survive as dark matter (Co et al., 2022). Another is late dissipation: in the dark-monopole model, a rotating QCD axion couples to a broken $\dot\theta$0 sector, dark monopoles become axion-dependent dyons, and repeated level crossings dissipate the axion’s rotational energy into dark fermions. In that framework, the same rotating axion can generate baryons and yield the correct dark matter abundance, with a characteristic bound

$\dot\theta$1

in the viable region (Co et al., 13 Nov 2025).

A second foundational tension concerns axion quality. The same explicit PQ breaking that is useful for spinning up the field can endanger the strong-CP solution. The axiverse proposal addresses this by making the QCD axion a linear combination of several axion-like fields, so that one direction can have large explicit breaking and efficient dissipation while another retains high PQ quality (Asadi et al., 19 Nov 2025). A different resolution is temporary explicit breaking: in axion cogenesis without isocurvature, large PQ breaking is effective only when the field sits near the Planck scale during inflation and becomes negligible later, so the late-time QCD axion remains high quality (Co et al., 2023).

Astrophysical bounds create a third tension because minimal axiogenesis often prefers $\dot\theta$2 well below the standard stellar-cooling window. One response is axion model building. The naturally astrophobic QCD axion suppresses couplings to nucleons, electrons, and muons by charge assignment, and when $\dot\theta$3 also suppresses the photon coupling. In that case, “minimal axiogenesis works,” with viable $\dot\theta$4 and axion mass above $\dot\theta$5 eV (Badziak et al., 2023). Another response is cosmological rather than hadronic: electroweak symmetry non-restoration in a supersymmetric Twin Higgs model raises the weak sphaleron freeze-out temperature and relaxes the bound on $\dot\theta$6, with a representative benchmark around $\dot\theta$7 GeV and a corresponding minimal-axiogenesis estimate $\dot\theta$8 GeV for $\dot\theta$9 GeV (Badziak et al., 21 Aug 2025).

5. Plasma effects, magnetic helicity, and observational implications

A major revision of the original picture arises once plasma instabilities are included. In “Baryogenesis from Decaying Magnetic Helicity in Axiogenesis,” the rotating-axion setup generically produces Standard Model chiral asymmetries large enough to trigger a chiral plasma instability or a direct axion–hypercharge tachyonic instability, thereby generating helical hypermagnetic fields. The helicity is approximately conserved until the electroweak phase transition and then partially converted into baryon number. In that treatment, baryogenesis from decaying helicity is often much more efficient than the original direct sphaleron channel and can overproduce the baryon asymmetry unless the instability is only marginally effective (Co et al., 2022). This has become a central caveat: in some regions of parameter space, magnetic helicity is not a correction to axiogenesis but its dominant intermediary.

Rotating axions also support gravitational-wave phenomenology when coupled to dark photons. In the kinetic-misalignment regime, the same axion rotation that can source baryogenesis can also drive a tachyonic dark-photon instability and a stochastic gravitational-wave background. The resulting parameter-space studies identify regions where successful axiogenesis overlaps with prospective sensitivity of LISA, DECIGO-class interferometers, and IAXO, although the same dark-photon coupling that strengthens the gravitational-wave signal can reduce the axion angular velocity and suppress baryogenesis (Madge et al., 2021).

Supersymmetric realizations add further cosmological structure. In the minimal SUSY KSVZ model, a single radiatively stabilized PQ field can realize lepto-axiogenesis while also producing axion and neutralino dark matter, small but potentially testable $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$0, and modest entropy dilution. Successful baryogenesis occurs for $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$1 when $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$2 and $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$3 when $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$4 (Kawamura et al., 2021). In the light-right-handed-neutrino extension, the explicit dynamics of $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$5 lower the required saxion mass and reopen parameter space down to near current collider limits for superpartners (Barnes et al., 2024).

Phenomenologically, the subject now spans low-$Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$6 direct axion detection, beam-dump and rare-decay probes for heavy QCD axions, collider searches for $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$7 or hidden-valley states, indirect probes of mixed dark sectors, future CMB sensitivity to $Y_B^{\rm obs}\simeq 8.7\times 10^{-11},$8, and possibly stochastic gravitational waves (Co et al., 2022). This breadth reflects the fact that modern axiogenesis is no longer a single model but a family of linked baryogenesis and dark-sector constructions.

6. Scope of the term and nonstandard usages

In current high-energy and cosmological usage, “axiogenesis” overwhelmingly denotes baryogenesis from axion rotation. That meaning was formalized by the 2019 paper titled “Axiogenesis,” and most subsequent work either elaborates its transfer mechanism or repairs its cosmological tensions (Co et al., 2019). Within that literature, even closely related labels such as “axion cogenesis,” “lepto-axiogenesis,” or “minimal axiogenesis” preserve the same core structure: a rotating PQ field, anomalous charge transfer, and a shared origin for baryons and at least part of the axion relic density.

A separate usage appears in developmental biophysics. In “The sound of an axon’s growth,” the problem called axiogenesis is regulation of axon length during development. There the proposed mechanism is not cosmological but cellular: bidirectional molecular-motor transport generates delay-dependent oscillations, nonlinear intracellular filtering performs a spectral decomposition, and the resulting mean response controls actomyosin contractility and axon extension versus retraction (Folz et al., 2018). The shared term refers only to axon growth and has no conceptual overlap with axion cosmology.

A further nonstandard cosmological usage appears in “Experimental evidence of dark matter axions identical to solar axions and the absence of the ‘fifth’ carrier force for the Higgs field,” where “axiogenesis” denotes conversion of an initially large thermal hot-axion abundance into baryons plus a residual coherent warm-axion component (Rusov et al., 2023). Its own detailed characterization states that it does not present a standard Boltzmann treatment or a field-theoretic conversion calculation and is best read as a heuristic cosmological accounting framework rather than as a standard first-principles axiogenesis mechanism (Rusov et al., 2023).

In the mainstream arXiv literature, the dominant meaning of axiogenesis therefore remains sharply defined: the generation of baryon asymmetry from coherent axion or PQ-field rotation, with later work focused on the efficiency of charge transfer, the control of dark relic overproduction, and the construction of viable UV and thermal histories (Barnes et al., 2022).