UCSC-SOE-11-11: Nonparametric Reconstruction of the Dark Energy Equation of State from Diverse Data Sets

Tracy Holsclaw, Ujjaini Alam, Bruno Sanso, Herbie Lee, Katrin Heitmann, Salman Habib, and David Higdon
04/12/2011 09:00 AM
Applied Mathematics & Statistics
The cause for 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, we first have to characterize the phenomenon. If we assume that the acceleration is caused by some form of dark energy, it can be described by its dark energy equation of state w. It is a major aim of ongoing and upcoming cosmological surveys to measure the dark energy equation of state and a possible time dependence at high accuracy. Since we cannot measure w(z) directly, we have to develop powerful reconstruction methods to extract w(z) reliably with controlled error bars. We have recently introduced a new reconstruction method for w(z) based on Gaussian process modeling. This method can capture non-trivial time-dependencies in w(z) and most importantly 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 and show constraints on w(z). We find 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 data from future surveys. We find that baryon acoustic oscillation measurements by themselves already lead to remarkably good reconstruction results and the combination of different high-quality probes allows us to reconstruct w(z) very reliably with small error bounds.