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

Botao Li, Zhaoting Chen, Yi-Fu Cai, Yi Mao

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 $k_\text{CMB}≃0.0045\text{Mpc}^{−1}⁠$, 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 $\Delta A ≃ 0.2$ at $0.056≲k_\text{21cm}≲0.15\text{Mpc}^{−1}⁠$. This limit may be further improved by an order of magnitude as $\Delta A ≃ 0.01$ with a cosmic variance limited experiment such as the Omniscope.