Direct Determination of Expansion History Using Redshift Distortions

TL;DR

This paper proposes a method to directly determine the universe's expansion history from redshift distortions by leveraging the FLRW cosmological principle, avoiding reliance on detailed prior assumptions or external data.

Contribution

It introduces a novel approach that uses the FLRW prior to break degeneracies in redshift distortion measurements, enabling direct estimation of cosmic distances and expansion history.

Findings

Improved detectability of power spectra and distance measures.

Reduced dependence on prior assumptions and external data.

Enhanced ability to distinguish distance effects from redshift distortions.

Abstract

We investigate the direct determination of expansion history using redshift distortions without plugging into detailed cosmological parameters. The observed spectra in redshift space include a mixture of information: fluctuations of density-density and velocity-velocity spectra, and distance measures of perpendicular and parallel components to the line of sight. Unfortunately it is hard to measure all the components simultaneously without any specific prior assumption. Common prior assumptions include a linear/quasi-linear model of redshift distortions or a model for the shape of the power spectra, which eventually breaks down on small scales at later epochs where nonlinear structure formation disturbs coherent growth. The degeneracy breaking, between the effect of cosmic distances and redshift distortions for example, depends on the prior we assume. An alternative approach is to utilize the cosmological principle inscribed in the heart of the Friedmann-Lematre-Robertson-Walker (hereafter FLRW) universe, that is, the specific relation between the angular diameter distance and the Hubble parameter, in this degeneracy breaking. We show that utilizing this FLRW prior early in the step of distinguishing the distance effect from redshift distortions helps us improve the detectability of power spectra and distance measures with no leaning on a combination of other experiments.