We point out three correlated predictions of the axion monodromy inflation model : large amplitude of gravitational waves , suppression of power on horizon scales and on scales relevant for the formation of dwarf galaxies .
While these predictions are likely generic to models with oscillations in the inflaton potential , the axion monodromy model naturally accommodates the required running spectral index through Planck-scale corrections to the inflaton potential .
Applying this model to a combined data set of Planck , ACT , SPT , and WMAP low- \ell polarization cosmic microwave background ( CMB ) data , we find a best-fit tensor-to-scalar ratio r _ { 0.05 } = 0.07 ^ { +0.05 } _ { -0.04 } due to gravitational waves , which may have been observed by the BICEP2 experiment .
Despite the contribution of gravitational waves , the total power on large scales ( CMB power spectrum at low multipoles ) is lower than the standard \Lambda CDM cosmology with a power-law spectrum of initial perturbations and no gravitational waves , thus mitigating some of the tension on large scales .
There is also a reduction in the matter power spectrum of 20-30 % at scales corresponding to k = 10 ~ { } { Mpc } ^ { -1 } , which are relevant for dwarf galaxy formation .
This will alleviate some of the unsolved small-scale structure problems in the standard \Lambda CDM cosmology .
The inferred matter power spectrum is also found to be consistent with recent Lyman- \alpha forest data , which is in tension with the Planck-favored \Lambda CDM model with power-law primordial power spectrum .