Uncertainty on w from large-scale structure

TL;DR

This paper shows that local inhomogeneities can significantly affect measurements of dark energy's properties, implying that cosmological conclusions depend on local matter density assumptions.

Contribution

It introduces a model of local inhomogeneity affecting dark energy parameter estimates and demonstrates its impact on observational constraints.

Findings

Dark energy may not be a cosmological constant if we reside in an inhomogeneity.

Local matter density influences the inferred equation of state of dark energy.

Accounting for large-scale structure uncertainties is crucial for accurate cosmology.

Abstract

We find that if we live at the center of an inhomogeneity with total density contrast of roughly 0.1, dark energy is not a cosmological constant at 95% confidence level. Observational constraints on the equation of state of dark energy, w, depend strongly on the local matter density around the observer. We model the local inhomogeneity with an exact spherically symmetric solution which features a pressureless matter component and a dark-energy fluid with constant equation of state and negligible sound speed, that reaches a homogeneous solution at finite radius. We fit this model to observations of the local expansion rate, distant supernovae and the cosmic microwave background. We conclude that the possible uncertainty from large-scale structure has to be taken into account if one wants to progress towards not just precision but also accurate cosmology.