http://arxiv.org/abs/2012.14248
Although natural inflation is a theoretically well-motivated model for cosmic inflation, it is in tension with recent Planck cosmic microwave background anisotropy measurements. We present a way to alleviate this tension by considering a very weak nonminimal coupling of inflaton field to gravity, in both contexts of metric and Palatini formulations of gravity. We start with generic forms of coupling function, then take its simplest form to do phenomenological analysis. Our results show that such an extension can render natural inflation’s predictions in a good agreement with the Planck data. As long as the inflaton’s coupling to the Ricci scalar is $|\xi|\sim 10^{-3}$ and the symmetry breaking scale $f\gtrsim 2.0 M_{\mathrm{pl}}$, predictions of the model can stay inside $68\%$ CL allowed regions until the $f$ growing up to $7.7 M_{\mathrm{pl}}$, then only inside $95\%$ CL region when $f$ exceeds this value. The predictions from metric and Palatini theories are very similar due the simple form of the coupling function we use and the small magnitude of the coupling $\xi$. Successful reheating can also be realized in this model.
Y. Reyimuaji and X. Zhang
Tue, 29 Dec 20
17/66
Comments: 20 pages, 8 figures, one table
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