Wedge-avoidance Fisher forecasts for primordial features from dark-ages 21-cm power spectrum and bispectrum

Abstract

The Dark Ages offer a uniquely clean window on primordial physics, making the redshifted 21-cm signal a promising probe of inflation models. Forecasts for interferometric 21-cm measurements must account for foreground wedge avoidance, which removes a substantial fraction of Fourier modes, and this effect is especially severe at high redshifts. We develop a wedge-aware Fisher framework in which this mode loss is propagated directly into the variances of the anisotropic 21-cm power spectrum and reduced bispectrum. As a case study, we apply the method to forecast constraints on two inflation models with different oscillatory features, a resonant model and a step model, for a lunar far-side array including thermal noise. Since these features affect both the power spectrum and the bispectrum, we apply wedge avoidance to both forecasts and compare their constraining power on oscillatory amplitudes in these feature models. We find that wedge avoidance reduces available Fourier modes significantly in both observables, leading to much weaker constraints on inflationary features. This framework is broadly applicable to 21-cm power spectrum and bispectrum forecasts across redshifts and is particularly useful in regimes where foreground wedge effect is severe, such as the epoch of reionization and the higher-redshift Dark Ages.