Observing nulling of primordial correlations via the 21 cm signal

The 21cm 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 wavenumber $k_{\text{dip}}$. We consider scenarios wherein the null in the correlations occurs over wavenumbers $1\lesssim k_{\text{dip}}\lesssim 10{\mathrm{M}\mathrm{p}\mathrm{c}}^{-1}$, and examine the prospects of detecting such a damping in the HI signal due to the nulls at the level of power and bi-spectra in future observational missions.