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A Solvable Model for Anharmonic Evolution of Cosmic Axion Overdensitites

Karl Strobl·Thomas J. Weiler
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Abstract

We present analytic solutions to the spatially homogeneous axion field equation, using a model potential which strongly resembles the $(1-\cos θ)$ standard anharmonic potential. We find that the anharmonicity amplifies early universe axion density fluctuations, but only significantly so for relatively large initial misalignment angles. Enhancements of $\sim$ (2,3,4,13) result for $θ_{\rm in}\sim (0.85,0.90,0.95,0.99)\timesπ$. The large $θ$ result agrees with Lyth, and so validates his approximations.

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Karl Strobl, Thomas J. Weiler. 1994-10-12. A Solvable Model for Anharmonic Evolution of Cosmic Axion Overdensitites. https://arxiv.org/abs/astro-ph/9410038

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