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arXiv · 2405.13881

Natural Inflation with Exponentially Small Tensor-To-Scalar Ratio

Dario L. Lorenzoni·David I. Kaiser·Evan McDonough
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Abstract

We demonstrate that "natural inflation", also known as "axion inflation", can be compatible with Planck 2018 measurements of the cosmic microwave background, while predicting an exponentially small tensor-to-scalar ratio, e.g., $r\sim 10^{-15}$. The strong suppression of $r$ arises from dynamics of the radial component of the complex scalar field, whose phase is the axion. Such tiny values of $r$ remain well below the threshold for detection by CMB-S4 or Simons Observatory B-mode searches. The model is testable with the running $\alpha_s$ of the spectral index, which is within reach of next-generation CMB and large-scale structure experiments, motivating the running as a primary science goal for future experiments.

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Dario L. Lorenzoni, David I. Kaiser, Evan McDonough. 2024-05-22. Natural Inflation with Exponentially Small Tensor-To-Scalar Ratio. https://doi.org/10.1103/physrevd.110.l061302

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