Probing BAO studies with flat $\Lambda$CDM constraints

Abstract

One of the algorithms typically used for fitting anisotropic Baryon Acoustic Oscillations (BAO), $\alpha_{\perp}D_{M, \text{fid}}(z)/r_{d, \text{fid}}=D_{M}(z)/r_{d}$, provides an excellent fit as $z\Rightarrow 0$. Yet, at $ z_{\text{drag}} \simeq 1060$, $D_{M, \text{fid}}(1060)/r_{d, \text{fid}}\simeq D_{M}(1060)/r_{d}$. Since $\alpha_{\perp}$ does not change with increasing redshift, we conclude that the algorithms deviate from true solutions with increasing $z$. We investigate that departure through an assumption of a flat $\Lambda$CDM cosmology. At the relatively low redshifts at which isotropic BAO studies were performed, the divergence is smaller than study uncertainties. However, while the transverse measure, $\alpha_{\perp}$ provides a reliable value in real space, not corrupted by redshift distortion, the isotropic measure, $\alpha$, has a radial component, and is influenced by redshift distortion. That distortion recommends against the inclusion of isotropic studies in cosmological parameter evaluations. At the high redshifts of Ly$\alpha$ forest BAO studies, $z\sim$ 2.35, the deviations of the anisotropic BAO algorithms from the flat $\Lambda$CDM solutions give rise to markedly deceptive results. We replicate an example, in which those algorithms lead to a value of $\Omega_{m}$ which is more than 15 per cent lower than that of the flat $\Lambda$CDM cosmology computation. The BAO algorithms are inappropriate for the next generation of BAO studies. A flat $\Lambda$CDM analysis offers an alternative means of assessment.