The BICEP 2 results , when interpreted as a gravitational wave signal and combined with other CMB data , suggest a roll-off in power towards small scales in the primordial matter power spectrum .
Among the simplest possibilities is a running of the spectral index .
Here we show that the preferred level of running alleviates small-scale issues within the \Lambda CDM model , more so even than viable WDM models .
We use cosmological zoom-in simulations of a Milky Way-size halo along with full-box simulations to compare predictions among four separate cosmologies : a BICEP 2-inspired running index model ( \alpha _ { s } = -0.024 ) , two fixed-tilt \Lambda CDM models motivated by Planck , and a 2.6 keV thermal WDM model .
We find that the running BICEP 2 model reduces the central densities of large dwarf-size halos ( V _ { \mathrm { max } } \sim 30 - 80 { km } { s } ^ { -1 } ) and alleviates the too-big-to-fail problem significantly compared to our adopted Planck and WDM cases .
Further , the BICEP 2 model suppresses the count of small subhalos by \sim 50 \% relative to Planck models , and yields a significantly lower “ boost ” factor for dark matter annihilation signals .
Our findings highlight the need to understand the shape of the primordial power spectrum in order to correctly interpret small-scale data .