The Reality of Baryonic Acoustic Oscillations

The initial idea for baryonic acoustic oscillations (BAO) came about during early efforts to understand the origin of galaxies by studying perturbed versions of the Friedmann-Robertson-Walker (FRW) model. In more recent times, the emphasis has shifted to the idea that 2-point galaxy correlations embedded in the distribution of matter by the BAO could be used as a standard ruler to fix the parameters of cosmological models. In this paper, we first consider the actual business of extracting the correlation length from large data sets of measured galaxy locations. To facilitate this process, we introduce a much-improved method for extracting the correlation peak from the data set. Fundamental to this process in any model is the use of a fiducial cosmological model to transition from redshift space to comoving coordinate space where the correlations actually exist. The belief is that the correlation length so determined can then be reverted to redshift space to fix the parameters of cosmological models. We show, however, that this process is circular and hence of no value whatsoever for fixing model parameters. All one obtains are the parameters of the model used to transition to comoving space in the first place. Finally, we present simple arguments that show that the idea of BAO being responsible for the structure of the universe, i.e. the cosmic web, is unworkable.

Test of the Cosmic Transparency with the Baryon Acoustic Oscillation and Type Ia Supernova Data

We use the latest baryon acoustic oscillation and Union 2.1 type Ia supernova data to test the cosmic opacity between different redshift regions without assuming any cosmological models. It is found that the universe may be opaque between the redshift regions 0.35 0.44, 0.44 0.57 and 0.6-0.73 since the best fit values of cosmic opacity in these regions are positive, while a transparent universe is favored in the redshift region 0.57-0.63. However, in general, a transparent universe is still consistent with observations at the lo confidence level.

A brief review on cosmological analysis of galaxy surveys with multiple tracers

Galaxy redshift surveys are one of the key probes in modern cosmology.In the data analysis of galaxy surveys,the precision of the statistical measurement is primarily limited by the cosmic variance on large scales.Fortunately,this limitation can in principle be mitigated by observing multiple types of biased tracers.In this brief review,we present the idea of the multi-tracer method,outline key steps in the data analysis and show several worked examples based on the GAMA,BOSS and e BOSS galaxy surveys.This work is a part of a special issue dedicated to the 20 th anniversary of RAA(2001–2020),which is prefaced in Wang&Ip(2020).

Forecast for weighing neutrinos in cosmology with SKA

We investigate what role the SKA neutral hydrogen(HI)intensity mapping(IM)and galaxy sky surveys will play in weighing neutrinos in cosmology.We use the simulated data of the baryon acoustic oscillation(BAO)measurements from the HI surveys based on SKA1(IM)and SKA2(galaxy)to do the analysis.For the current observations,we use the Planck 2015 cosmic microwave background(CMB)anisotropies observation,the optical BAO measurements,the type Ia supernovae(SN)observation(Pantheon compilation),and the latest H0 measurement.We consider three mass ordering cases for massive neutrinos,i.e.,the normal hierarchy(NH),inverted hierarchy(IH),and degenerate hierarchy(DH)cases.It is found that the SKA observation can significantly improve the constraints on?m and H0.Compared to the current observation,the SKA1 data can improve the constraints on?m by about 33%,and on H0 by about 36%;the SKA2 data can improve the constraints on?m by about 58%,and on H0 by about 66%.It is also found that the SKA observation can only slightly improve the constraints on∑mν.Compared to the current observation,the SKA1 data can improve the constraints on∑mνby about 4%,3%,and 10%,for the NH,IH,and DH cases,respectively;the SKA2 data can improve the constraints on∑mνby about 7%,7%,and 16%,for the NH,IH,and DH cases,respectively.