Supersymmetry can stabilize an ultralight dilaton dark matter candidate, but gravity restricts its Standard Model couplings to undetectable levels, making consistent model building involved.
Anharmonic Evolution of the Cosmic Axion Density Spectrum
3 Pith papers cite this work, alongside 41 external citations. Polarity classification is still indexing.
abstract
We present analytic solutions to the spatially homogeneous axion field equation, using a model potential which strongly resembles the standard anharmonic $(1-\cos N\theta)$ potential, but contains only a piece-wise second order term. Our exactly soluble model for $\theta(t)$ spans the entire range $[-\pi/N,\pi/N]$. In particular, we are able to confirm (i) Turner's numeric correction factors \cite{Turner} to the adiabatic and harmonic analytic treatments of homogeneous axion oscillations, and (ii) Lyth's estimate \cite{Lyth} valid near the metastable misalignment angle $\pi/N$ at the peak of the potential. We compute the enhancement of axion density fluctuations that occurs when the axion mass becomes significant at $T\sim 1$ GeV. We find that the anharmonicity amplifies density \mbox{f}luctuations, but only significantly for relatively large initial misalignment angles. The enhancement factor is $\sim$ (2,3,4,13) for $\theta_{\rm in}\sim (0.85,0.90,0.95,0.99)\times\pi$.
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Combined CMB datasets moderately tighten the allowed range for the spectral index of axion isocurvature but leave amplitude bounds for fixed indices unchanged.
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