# Axion misalignment driven to the bottom

## Abstract

Several theoretical motivations point to ultralight QCD axions with large decay constants $$f_a \simeq \mathcal{O}(10^{16}-10^{17})$$ 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 $$\theta_{\rm mis}$$ is as small as $$\mathcal{O}(10^{-3}-10^{-4})$$, which is generally considered a fine-tuning problem. We investigate a dynamical explanation for a small $$\theta_{\rm mis}$$. 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 $$\theta_{\rm mis}$$ 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.

- Authors:

- Univ. of Michigan, Ann Arbor, MI (United States). Leinweber Center for Theoretical Physics
- Inst. for Advanced Study, Princeton, NJ (United States)

- Publication Date:

- Research Org.:
- Inst. for Advanced Study, Princeton, NJ (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC)

- OSTI Identifier:
- 1596298

- Grant/Contract Number:
- SC0009988; SC0019225

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of High Energy Physics (Online)

- Additional Journal Information:
- Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2019; Journal Issue: 5; Journal ID: ISSN 1029-8479

- Publisher:
- Springer Berlin

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 79 ASTRONOMY AND ASTROPHYSICS; Cosmology of Theories beyond the SM; Con finement; Supersymmetric Gauge Theory; Supersymmetric Standard Model

### Citation Formats

```
Co, Raymond T., Gonzalez, Eric, and Harigaya, Keisuke. Axion misalignment driven to the bottom. United States: N. p., 2019.
Web. doi:10.1007/JHEP05(2019)162.
```

```
Co, Raymond T., Gonzalez, Eric, & Harigaya, Keisuke. Axion misalignment driven to the bottom. United States. doi:10.1007/JHEP05(2019)162.
```

```
Co, Raymond T., Gonzalez, Eric, and Harigaya, Keisuke. Mon .
"Axion misalignment driven to the bottom". United States. doi:10.1007/JHEP05(2019)162. https://www.osti.gov/servlets/purl/1596298.
```

```
@article{osti_1596298,
```

title = {Axion misalignment driven to the bottom},

author = {Co, Raymond T. and Gonzalez, Eric and Harigaya, Keisuke},

abstractNote = {Several theoretical motivations point to ultralight QCD axions with large decay constants $f_a \simeq \mathcal{O}(10^{16}-10^{17})$ 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 $\theta_{\rm mis}$ is as small as $\mathcal{O}(10^{-3}-10^{-4})$, which is generally considered a fine-tuning problem. We investigate a dynamical explanation for a small $\theta_{\rm mis}$. 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 $\theta_{\rm mis}$ 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.},

doi = {10.1007/JHEP05(2019)162},

journal = {Journal of High Energy Physics (Online)},

number = 5,

volume = 2019,

place = {United States},

year = {2019},

month = {5}

}

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