Nonparametric Reconstruction of the Dark Energy Equation of State from Diverse Data Sets

TL;DR

This paper introduces an advanced Gaussian process-based method for reconstructing the dark energy equation of state from diverse cosmological data, demonstrating its effectiveness with current and simulated future observations.

Contribution

It extends a Gaussian process reconstruction method to incorporate multiple data types, providing reliable, unbiased estimates of w(z) and its potential nontrivial behavior.

Findings

Current data agree with a cosmological constant.

BAO measurements alone yield good reconstruction results.

Combining multiple high-quality probes improves accuracy and reliability.

Abstract

The cause of the accelerated expansion of the Universe poses one of the most fundamental questions in physics today. In the absence of a compelling theory to explain the observations, a first task is to develop a robust phenomenology. If the acceleration is driven by some form of dark energy, then, the phenomenology is determined by the dark energy equation of state w. A major aim of ongoing and upcoming cosmological surveys is to measure w and its time dependence at high accuracy. Since w(z) is not directly accessible to measurement, powerful reconstruction methods are needed to extract it reliably from observations. We have recently introduced a new reconstruction method for w(z) based on Gaussian process modeling. This method can capture nontrivial time-dependences in w(z) and, most importantly, it yields controlled and unbaised error estimates. In this paper we extend the method to include a diverse set of measurements: baryon acoustic oscillations, cosmic microwave background measurements, and supernova data. We analyze currently available data sets and present the resulting constraints on w(z), finding that current observations are in very good agreement with a cosmological constant. In addition we explore how well our method captures nontrivial behavior of w(z) by analyzing simulated data assuming high-quality observations from future surveys. We find that the baryon acoustic oscillation measurements by themselves already lead to remarkably good reconstruction results and that the combination of different high-quality probes allows us to reconstruct w(z) very reliably with small error bounds.