# Concordance Cosmology?

## TL;DR

This paper introduces a new metric to evaluate tensions between cosmological data sets, finds a modest tension between DES Year 1 and Planck CMB data, and discusses implications for the standard cosmological model.

## Contribution

It proposes an intuitive, robust metric for assessing experiment tension and applies it to cosmological data, revealing a modest discrepancy in structure measurements.

## Key findings

- 2.2σ tension between DES Year 1 and Planck CMB data
- Tension driven by differences in structure growth, unrelated to Hubble rate discrepancies
- Reconciling all data may require modifications to the flat ΛCDM model in early and late Universe physics

## Abstract

We propose a new intuitive metric for evaluating the tension between two experiments, and apply it to several data sets. While our metric is non-optimal, if evidence of tension is detected, this evidence is robust and easy to interpret. Assuming a flat $\Lambda$CDM cosmological model, we find that there is a modest $2.2\sigma$ tension between the DES Year 1 results and the ${\it Planck}$ measurements of the Cosmic Microwave Background (CMB). This tension is driven by the difference between the amount of structure observed in the late-time Universe and that predicted from fitting the ${\it Planck}$ data, and appears to be unrelated to the tension between ${\it Planck}$ and local esitmates of the Hubble rate. In particular, combining DES, Baryon Acoustic Oscillations (BAO), Big-Bang Nucleosynthesis (BBN), and supernovae (SNe) measurements recovers a Hubble constant and sound horizon consistent with ${\it Planck}$, and in tension with local distance-ladder measurements. If the tension between these various data sets persists, it is likely that reconciling ${\it all}$ current data will require breaking the flat $\Lambda$CDM model in at least two different ways: one involving new physics in the early Universe, and one involving new late-time Universe physics.