Abstract
ABSTRACT Quantifying tensions – inconsistencies amongst measurements of cosmological parameters by different experiments – has emerged as a crucial part of modern cosmological data analysis. Statistically significant tensions between two experiments or cosmological probes may indicate new physics extending beyond the standard cosmological model and need to be promptly identified. We apply several tension estimators proposed in the literature to the dark energy survey (DES) large-scale structure measurement and Planck cosmic microwave background data. We first evaluate the responsiveness of these metrics to an input tension artificially introduced between the two, using synthetic DES data. We then apply the metrics to the comparison of Planck and actual DES Year 1 data. We find that the parameter differences, Eigentension, and Suspiciousness metrics all yield similar results on both simulated and real data, while the Bayes ratio is inconsistent with the rest due to its dependence on the prior volume. Using these metrics, we calculate the tension between DES Year 1 3 × 2pt and Planck, finding the surveys to be in ∼2.3σ tension under the ΛCDM paradigm. This suite of metrics provides a toolset for robustly testing tensions in the DES Year 3 data and beyond.
Highlights
Two experiments are generally expected to agree, roughly within the reported errors, on the measured values of cosmological parameters
We have explored different methods to quantify consistency between two uncorrelated data sets, focusing on the comparison between Dark Energy Survey (DES) and Planck
The motivation is to decide on a metric of tension between these two surveys ahead of the DES Y3 data release
Summary
Two experiments are generally expected to agree, roughly within the reported errors, on the measured values of cosmological parameters. A disagreement between such measurements — a tension — may be a sign of a mistake in one or both analyses, of unaccounted-for systematic errors, or perhaps of new physics. A prominent historical example of such tensions in cosmology is the disagreement between a variety of measurements of the matter density Ωm in the 1980s and 1990s that was vigorously debated at the time (Peebles 1984; Efstathiou et al 1990; Ostriker & Steinhardt 1995; Krauss & Turner 1995) and eventually turned out to be explained by the discovery of the accelerating universe (Perlmutter et al 1999; Riess et al 1998). The discrepancy between the measurements of the Hubble constant using the distance ladder, H0 = (74.03 ± 1.42) km/s/Mpc (Riess et al 2019), and those from Planck, H0 = (67.4 ± 0.5) km/s/Mpc (Planck Collaboration 2018), is much discussed, as it may be a harbinger of new physics. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No DE-AC02-07CH11359
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