Testing the scale-dependent hemispherical asymmetry with the 21-cm power spectrum from the epoch of reionization

Abstract

Abstract Hemispherical power asymmetry has emerged as a new challenge to cosmology in early Universe. While the cosmic microwave background (CMB) measurements indicated the asymmetry amplitude A ≃ 0.07 at the CMB scale $k_{\rm CMB}\simeq 0.0045\, {\rm Mpc}^{-1}$, the high-redshift quasar observations found no significant deviation from statistical isotropy. This conflict can be reconciled in some scale-dependent asymmetry models. We put forwards a new parametrization of scale-dependent asymmetric power spectrum, inspired by a multispeed inflation model. The 21-cm power spectrum from the epoch of reionization can be used to constrain the scale-dependent hemispherical asymmetry. We demonstrate that an optimum, multifrequency observation by the Square Kilometre Array (SKA) Phase 2 can impose a constraint on the amplitude of the power asymmetry anomaly at the level of ΔA ≃ 0.2 at $0.056 \lesssim k_{\rm 21cm} \lesssim 0.15 \, {\rm Mpc}^{-1}$. This limit may be further improved by an order of magnitude as ΔA ≃ 0.01 with a cosmic variance limited experiment such as the Omniscope.