http://arxiv.org/abs/1812.08754
We consider Higgs inflation with an $\alpha R^2$ term. This term adds a new scalar degree of freedom, which leads to a two-field model of inflation. We do a complete slow-roll analysis of the three-dimensional parameter space of the $R^2$ coefficient $\alpha$, the non-minimal coupling $\xi$ and the Higgs self-coupling $\lambda$. We find three classes of different inflationary solutions. We also find that pure Higgs inflation is impossible when the $R^2$ term is present regardless of how small $\a$ is. However, in some cases we can have Higgs-like inflation, in which the amplitude is independent of $\alpha$. The spectral index for the model can have any value within the range of Planck results, and constraining it to the observed range, the tensor-to-scalar ratio is $3.8\times10^{-3} < r < 0.053$. The upper bound of $r$ comes from to the observational upper bound on the running of the spectral index $\alpha_R$. We also calculate the non-Gaussianity parameter $f_{\rm NL}$ and isocurvature perturbations, and find they are within the observational limits.
V. Enckell, K. Enqvist, S. Rasanen, et. al.
Fri, 21 Dec 18
35/72
Comments: 18 pages, 5 figures
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