Axion misalignment driven to the hilltop

Journal Article · 26 May 2019 · Journal of High Energy Physics (Online)

DOI: https://doi.org/10.1007/JHEP05(2019)163 · OSTI ID:1596295

Co, Raymond T. ^[1]; Gonzalez, Eric  ^[2]; Harigaya, Keisuke ^[3]

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1. Univ. of Michigan, Ann Arbor, MI (United States). Leinweber Center for Theoretical Physics; Institute for Advanced Study
2. Univ. of Michigan, Ann Arbor, MI (United States). Leinweber Center for Theoretical Physics
3. Inst. for Advanced Study, Princeton, NJ (United States)

The QCD axion serves as a well-motivated dark matter candidate and the misalignment mechanism is known to reproduce the observed abundance with a decay constant $$f_a \simeq \mathcal{O}(10^{12})$$ GeV for a misalignment angle $$\theta_{\rm mis} \simeq \mathcal{O}(1)$$. While $$f_a \ll 10^{12}$$ GeV is of great experimental interest, the misalignment mechanism requires the axion to be very close to the hilltop, i.e. $$\theta_{\rm mis} \simeq \pi$$. This particular choice of $$\theta_{\rm mis}$$ has been understood as fine-tuning the initial condition. We offer a dynamical explanation for $$\theta_{\rm mis} \simeq \pi$$ in a class of models. The axion dynamically relaxes to the minimum of the potential by virtue of an enhanced mass in the early universe. This minimum is subsequently converted to a hilltop because the CP phase of the theory shifts by $$\pi$$ when one contribution becomes subdominant to another with an opposite sign. We demonstrate explicit and viable examples in supersymmetric models where the higher dimensional Higgs coupling with the inflaton naturally achieves both criteria. Associated phenomenology includes a strikingly sharp prediction of $$3 \times 10^9$$ GeV $$\lesssim f_a \lesssim 10^{10}$$ GeV and the absence of isocurvature perturbation.

• Research Organization: Inst. for Advanced Study, Princeton, NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0009988; SC0019225
• OSTI ID: 1596295
• Journal Information: Journal of High Energy Physics (Online), Journal Name: Journal of High Energy Physics (Online) Journal Issue: 5 Vol. 2019; ISSN 1029-8479
• Publisher: Springer BerlinCopyright Statement
• Country of Publication: United States
• Language: English