Model-Independent Dark Energy Equation of State from Unanchored Baryon Acoustic Oscillations

TL;DR

This paper introduces a model-independent method using BAO ratios to probe dark energy, revealing a significant tension with the standard LambdaCDM model based on Lyman alpha forest measurements.

Contribution

It demonstrates that BAO ratios can independently test dark energy evolution without relying on cosmic distance anchors or early universe assumptions.

Findings

Over 3 sigma tension with LambdaCDM from BAO ratios

Potential systematic issues in Lyman alpha forest measurements

Indication of steep dark energy equation of state at high redshift

Abstract

Ratios of line of sight baryon acoustic oscillation (BAO) peaks at two redshifts only depend upon the average dark energy equation of states between those redshifts, as the dependence on anchors such as the BAO scale or the Hubble constant is canceled in a ratio. As a result, BAO ratios provide a probe of dark energy which is independent of both the cosmic distance ladder and the early evolution of universe. In this note, we use ratios to demonstrate that the known tension between the Lyman alpha forest BAO measurement and other probes arises entirely from recent (0.57<z<2.34) cosmological expansion. Using ratios of the line of sight Lyman alpha forest and BOSS CMASS BAO scales, we show that there is already more than 3 sigma tension with the standard LambdaCDM cosmological model which implies that either (i) The BOSS Lyman alpha forest measurement of the Hubble parameter was too low as a result of a statistical fluctuation or systematic error or else (ii) the dark energy equation of state falls steeply at high redshift.