Cosmological parameter measurement and neutral hydrogen 21 cm sky survey with the Square Kilometre Array
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July 2020 Vol. 63 No. 7: 270431 https://doi.org/10.1007/s11433-020-1544-3
Cosmological parameter measurement and neutral hydrogen 21 cm sky survey with the Square Kilometre Array YiDong Xu1, and Xin Zhang2* 1 Key
Laboratory for Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China; 2 Department of Physics, College of Sciences, Northeastern University, Shenyang 110819, China Received March 5, 2020; accepted March 12, 2020; published online April 10, 2020
Citation:
Y. D. Xu, and X. Zhang, Cosmological parameter measurement and neutral hydrogen 21 cm sky survey with the Square Kilometre Array, Sci. China-Phys. Mech. Astron. 63, 270431 (2020), https://doi.org/10.1007/s11433-020-1544-3
Through decades of continuous efforts by the whole community of cosmology, a standard cosmological model known as the Λ cold dark matter (ΛCDM) model has been established, in which the total energy budget consists of 5% ordinary matter, 27% cold dark matter, and 68% dark energy described by a cosmological constant Λ, and the inflation process in the very early universe yielded adiabatic, Gaussian, nearly scale-invariant primordial density perturbations, and possibly detectable primordial gravitational waves. The ΛCDM model with several ansatzes can fit the observational data of cosmology with breathtaking precision. Actually, the Planck satellite mission has implemented unprecedentedly precise measurements for the cosmic microwave background (CMB) anisotropies, and the latest observational results of the CMB power spectra strongly favor a “base” version of the ΛCDM model that has only six basic cosmological parameters and a number of well-tested ansatzes. However, although the base-ΛCDM cosmology seems to be able to explain various cosmological observations quite well, some cracks still appear in the model. Recently, it was found that the Planck results for the baseΛCDM cosmology are in tension with some low-redshift observations. For example, the amplitude of the fluctuation spectrum in the base-ΛCDM cosmology, constrained by the Planck observation, is found to be higher than that inferred from some analyses of cluster counts, weak *Corresponding author (email: [email protected])
gravitational lensing, and galaxy clustering; more importantly, the Planck base-ΛCDM results are in significant, 4-6σ, tension with local measurements of the Hubble constant (which prefer a higher value) [1]. These discrepancies in observations imply that the current standard model of cosmology is tantalizingly incomplete, and needs to be extended. Theorists have designed a variety of wild theories beyond the standard model, introducing new physics and additional parameters into the extended models. Nevertheless, the CMB observation is a two-dimensional measurement of the early universe, and thus cannot provide tight constraints on the parameters that concern the physical effects of the late universe. The CMB-alone constraints will always lead to significa
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