Observing Nulling of Primordial Correlations via the 21-cm Signal.

The 21-cm line emitted by neutral hydrogen (HI) during the Dark Ages carries imprints of pristine primordial correlations. In models of inflation driven by a single, canonical scalar field, we show that a phase of ultra-slow-roll can lead to a null in all the primordial correlations at a specific wave number k_{dip}. We consider scenarios wherein the null in the correlations occurs over wave numbers 1≲k_{dip}≲10  Mpc^{-1}, and examine the prospects of detecting such a damping in the HI signal due to the nulls at the level of power and bispectra in future observational missions.