Several theoretical motivations point to ultralight QCD axions with large decay constants fa≃O(1016−1017)GeV, to which experimental proposals are dedicated. This regime is known to face the problem of overproduction of axion dark matter from the misalignment mechanism unless the misalignment angle θmis is as small as O(10 − 3− 10 − 4) , which is generally considered a fine-tuning problem. We investigate a dynamical explanation for a small θmis. The axion mass arises from strong dynamics and may be sufficiently enhanced by early dynamics so as to overcome Hubble friction and drive the field value to the bottom of the potential long before the QCD phase transition. Together with an approximate CP symmetry in the theory, this minimum is very closely related to today’s value and thus θmis can automatically be well under unity. Owing to such efficient relaxation, the isocurvature perturbations are essentially damped. As an existence proof, using supersymmetric theories we illustrate that the Higgs coupling with the inflaton energy can successfully achieve this axion damping in a consistent inflationary cosmology.
Bibliographical noteFunding Information:
Article funded by SCOAP3.
© 2019, The Author(s).
- Cosmology of Theories beyond the SM
- Supersymmetric Gauge Theory
- Supersymmetric Standard Model