We forecast constraints on cosmological parameters in the interacting dark energy models using the mock data generated for neutral hydrogen intensity mapping (IM) experiments. In this work, we only consider the interacting dark energy models with energy transfer rate Q = β H ρ c and take BINGO, FAST, SKA1-MID, and Tianlai as typical examples of the 21 cm IM experiments. We find that the Tianlai cylinder array will play an important role in constraining the interacting dark energy model. Assuming perfect foreground removal and calibration and using the Tianlai-alone data, we obtain σ(H 0) = 0.19 km s−1 Mpc−1, σ(Ω m ) = 0.0033, and σ(σ 8) = 0.0033 in the IΛCDM model, which are much better than the results of Planck+optical BAO (i.e., optical galaxy surveys). However, the Tianlai-alone data cannot provide a very tight constraint on the coupling parameter β compared with Planck+optical BAO, while the Planck+Tianlai data can give a rather tight constraint of σ(β) = 0.00023 due to the parameter degeneracies being well broken by the data combination. In the IwCDM model, we obtain σ(β) = 0.00079 and σ(w) = 0.013 from Planck+Tianlai. In addition, we also make a detailed comparison among BINGO, FAST, SKA1-MID, and Tianlai in constraining the interacting dark energy models. We show that future 21 cm IM experiments will provide a useful tool for exploring the nature of dark energy and play a significant role in measuring the coupling between dark energy and dark matter.

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Abstract. The past, present and future of cosmic microwave background (CMB) anisotropy research is discussed, with emphasis on the Boomerang and Maxima balloon experiments. These data are combined with large scale structure (LSS) information derived from local cluster abundances and galaxy clustering and high redshift supernova (SN1) observations to explore the inflation-based cosmic structure formation paradigm. Here we primarily focus on a simplified inflation parameter set,After marginalizing over the other cosmic and experimental variables, we find the current CMB+LSS+SN1 data gives Ω tot = 1.04±0.05, consistent with (non-baroque) inflation theory. Restricting to Ω tot = 1, we find a nearly scale invariant spectrum, n s = 1.03 ± 0.07. The CDM density, ω cdm = 0.17 ± 0.02, is in the expected range, but the baryon density, ω b ≡ Ω b h 2 = 0.030 ± 0.004, is slightly larger than the current 0.019 ± 0.002 Big Bang Nucleosynthesis estimate. Substantial dark (unclustered) energy is inferred, Ω Q ≈ 0.68 ± 0.05, and CMB+LSS Ω Q values are compatible with the independent SN1 estimates. The dark energy equation of state, parameterized by a quintessence-field pressure-to-density ratio w Q , is not well determined by CMB+LSS (w Q < −0.3 at 95% CL), but when combined with SN1 the resulting w Q < −0.7 limit is quite consistent with the w Q =−1 cosmological constant case. Though forecasts of statistical errors on parameters for current and future experiments are rosy, rooting out systematic errors will define the true progress. CMB ANALYSIS: PAST, PRESENT AND FUTUREThe CMB is a nearly perfect blackbody of 2.725 ± 0.002 K [1], with a 3.372 ± 0.007 mK dipole associated with the 300 km s −1 flow of the earth in the CMB, and a rich pattern of higher multipole anisotropies at tens of µK arising from fluctuations at photon decoupling and later. Spectral distortions from the blackbody associated with starbursting galaxies detected in the COBE FIRAS and DIRBE data are due to stellar and accretion disk radiation being downshifted into the infrared by

Using the 21 cm intensity mapping (IM) technique can efficiently perform large-scale neutral hydrogen (HI) surveys, and this method has great potential for measuring dark-energy parameters. Some 21 cm IM experiments aiming at measuring dark energy in the redshift range of 0<z<3 have been proposed and performed, in which the typical ones using single-dish mode include e.g., BINGO, FAST, and SKA1-MID, and those using interferometric mode include e.g., HIRAX, CHIME, and Tianlai. In this work, we make a forecast for these typical 21 cm IM experiments on their capability of measuring parameters of dark energy. We find that the interferometers have great advantages in constraining cosmological parameters. In particular, the Tianlai cylinder array alone can achieve the standard of precision cosmology for the ΛCDM model (i.e., the precision of parameters is better than 1%). However, for constraining dynamical dark energy, we find that SKA1-MID performs very well. We show that the simulated 21 cm IM data can break the parameter degeneracies inherent in the CMB data, and CMB+SKA1-MID offers σ(w)=0.013 in the wCDM model, and σ(w 0)=0.080 and σ(w a)=0.25 in the CPL model. Compared with CMB+BAO+SN, Tianlai can provide tighter constraints in ΛCDM and wCDM, but looser constraints (tighter than CMB+BAO) in CPL, and the combination CMB+BAO+SN+Tianlai gives σ(w)=0.013, σ(w 0)=0.055, and σ(w a)=0.13. In addition, it is found that the synergy of FAST (0<z<0.35)+SKA1-MID (0.35<z<0.77)+Tianlai (0.77<z<2.55) offers a very promising survey strategy. Finally, we find that the residual foreground contamination amplitude has a considerable impact on constraint results. We show that in the future 21 cm IM experiments will provide a powerful probe for exploring the nature of dark energy.

The reionization process is expected to be prolonged by the small-scale absorbers (SSAs) of ionizing photons, which have been seen as Lyman-limit systems in quasar absorption line observations. We use a set of semi-numerical simulations to investigate the effects of absorption systems on the reionization process, especially their impacts on the neutral islands during the late epoch of reionization (EoR). Three models are studied, i.e., the extreme case of no-SSA model with a high level of ionizing background, the moderate-SSA model with a relatively high level of ionizing background, and the dense-SSA model with a low level of ionizing background. We find that while the characteristic scale of neutral regions decreases during the early and middle stages of reionization, it stays nearly unchanged at about 10 co-moving Mpc during the late stage for the no-SSA and moderate-SSA models. However, in the case of weak ionizing background in the dense-SSA model, the characteristic island scale shows obvious evolution, as large islands break into many small ones that are slowly ionized. The evolutionary behavior of neutral islands during the late EoR thus provides us with a novel way to constrain the abundance of SSAs. We discuss the 21 cm observation with the upcoming Square Kilometre Array. The different models can be distinguished by either the 21 cm imaging or the 21 cm power spectrum measurements.