Abstract
We revisit large field inflation models with modulations in light of the recent discovery of the primordial B-mode polarization by the BICEP2 experiment, which, when combined with the Planck+WP+highL data, gives a strong hint for additional suppression of the CMB temperature fluctuations at small scales. Such a suppression can be explained by a running spectral index. In fact, it was pointed out by two of the present authors (TK and FT) that the existence of both tensor mode perturbations and a sizable running of the spectral index is a natural outcome of large inflation models with modulations such as axion monodromy inflation. We find that this holds also in the recently proposed multi-natural inflation, in which the inflaton potential consists of multiple sinusoidal functions and therefore the modulations are a built-in feature.
Highlights
We revisit large field inflation models with modulations in light of the recent discovery of the primordial B-mode polarization by the BICEP2 experiment, which, when combined with the Planck + WP + highL data, gives a strong hint for additional suppression of the cosmic microwave background (CMB) temperature fluctuations at small scales
If the primordial B-mode polarization is measured with better accuracy by the Planck satellite and other ground-based experiments, it will pin down the underlying inflation model, providing invaluable information on the UV physics such as string theory
The BICEP2 data, when combined with the Planck+WP+highL data, gives a strong hint for some additional suppression of the CMB temperature fluctuations at small scales [1]. This is because the large tensor mode perturbations contribute to the CMB temperature fluctuations at large scales, which causes the tension on the relative size of scalar density perturbations at large and small scales
Summary
The BICEP2 experiment detected the primordial B-mode polarization of the cosmic microwave background (CMB) with very high significance [1], giving a very strong case for inflation [2, 3]. [38], two of the present authors (TK and FT) showed that a sizable running spectral index can be realized without significant impact on the overall behavior of the inflaton if there are small modulations on the inflaton potential. Modulations, the inflaton field excursion must be relatively large as in the large-field inflation Both the tensor mode and the running spectral index are a natural outcome of the large field inflation with modulations. Examples such as monomial inflaton potentials (V = λφn) with superimposed periodic oscillations were studied in [38]. We show that the negative running spectral index can be realized without significant impact on the overall inflation dynamics, similar to the case studied before. We will show that the predicted values of (ns, r) for quadratic chaotic inflation and natural inflation can be realized in multi-natural inflation
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