Beating non-linearities: improving the baryon acoustic oscillations with the linear point

Abstract

We propose a new way of looking at the Baryon Acoustic Oscillations in the Large Scale Structure clustering correlation function. We identify a scale s LP that has two fundamental features: its position is insensitive to non-linear gravity, redshift space distortions, and scale-dependent bias at the 0.5% level; it is geometrical, i.e. independent of the power spectrum of the primordial density fluctuation parameters. These two properties together make s LP , called the "linear point", an excellent cosmological standard ruler. The linear point is also appealing because it is easily identified irrespectively of how non-linearities distort the correlation function. Finally, the correlation function amplitude at s LP is similarly insensitive to non-linear corrections to within a few percent. Hence, exploiting the particular Baryon features in the correlation function, we propose three new estimators for growth measurements. A preliminary analysis of s LP in current data is encouraging.

Linear point and sound horizon as purely geometric standard rulers

“…1 for ω b , ωc and ns. As expected [14], non-linear physics reduces sLP at z=0 to ∼ 99% of its high-z value for the fiducial cosmology, motivating a 0.5% correction to keep s non−lin LP within 0.5% of s lin LP over the full range of redshift values.…”

“…3, we display the rulers' dependence for 0.5 < n s < 2. The n s dependence of the LP is still within the 0.5% LP intrinsic uncertainty [14], and can thus be neglected in the cosmological analysis. For n s > 2, this no longer the case.…”

“…In [14] it was proved that the LP has a 0. body simulations, and cross-checked with a simple nonlinear CF model. Since in [14] the analysis was performed for one set of cosmological parameters, it is important to test here whether the 0.5% intrinsic uncertainty holds within the considered 10σ range around Planck values.…”

“…This is not a problem, as to estimate the LP from the data we employ a procedure that is independent of both any two-point-CF model and of the cosmology. We can therefore perform a conditional cosmological analysis: if the LP is detected then n s > 0.5 14 . This has the advantage of providing an immediate lower limit on n s no matter the ab initio prior.…”

Cosmic distance inference from purely geometric BAO methods: Linear point standard ruler and correlation function model fitting

“…In [19], the authors have shown that the Linear Point standard ruler (LP) provides a PG-BAO method, as it precisely shares all the (A) requirements. It is defined as the mid-point between the BAO peak and the dip of the 2-point correlation function.…”