TY  - JOUR
PB  - SciPost Foundation
DO  - 10.21468/SciPostPhys.18.6.175
TI  - Cosmology of the companion-axion model: Dark matter, gravitational waves, and primordial black holes
PY  - 2025/06/04
UR  - https://scipost.org/SciPostPhys.18.6.175
JF  - SciPost Physics
JA  - SciPost Phys.
VL  - 18
IS  - 6
SP  - 175
A1  - Chen, Zhe
AU  - Kobakhidze, Archil
AU  - O'Hare, Ciaran
AU  - Picker, Zachary
AU  - Pierobon, Giovanni
AB  - The companion-axion model introduces a second QCD axion to rescue the Peccei-Quinn solution to the strong-CP problem from the effects of colored gravitational instantons. As in single-axion models, the two axions predicted by the companion-axion model are attractive candidates for dark matter. The model is defined by two free parameters, the scales of the two axions' symmetry breaking, so we can classify production scenarios in terms of the relative sizes of these two scales with respect to the scale of inflation. We study the cosmological production of companion-axion dark matter in order to predict windows of preferred axion masses, and calculate the relative abundances of the two particles. Additionally, we show that the presence of a second axion solves the cosmological domain wall problem automatically in the scenarios in which one or both of the axions are post-inflationary. We also suggest unique cosmological signatures of the companion-axion model, such as the production of a $\sim$10 nHz gravitational wave background, and $\sim 100\,M_\odot$ primordial black holes.
ER  -

@Article{10.21468/SciPostPhys.18.6.175,
	title={{Cosmology of the companion-axion model: Dark matter, gravitational waves, and primordial black holes}},
	author={Zhe Chen and Archil Kobakhidze and Ciaran O'Hare and Zachary S. C. Picker and Giovanni Pierobon},
	journal={SciPost Phys.},
	volume={18},
	pages={175},
	year={2025},
	publisher={SciPost},
	doi={10.21468/SciPostPhys.18.6.175},
	url={https://scipost.org/10.21468/SciPostPhys.18.6.175},
}