Simultaneous Falsification of LCDM and Quintessence with Massive, Distant Clusters

TL;DR

This paper assesses whether current massive, distant galaxy clusters can falsify the standard LCDM and quintessence cosmological models, finding that current data and uncertainties do not exclude these models.

Contribution

It provides a likelihood framework and fitting formulas to evaluate the falsifiability of LCDM and quintessence models using cluster observations.

Findings

Current clusters do not falsify LCDM or quintessence models.

Systematic uncertainties in mass measurements are the main limiting factor.

Falsification requires observing clusters with masses three times larger than typical expectations.

Abstract

Observation of even a single massive cluster, especially at high redshift, can falsify the standard cosmological framework consisting of a cosmological constant and cold dark matter (LCDM) with Gaussian initial conditions by exposing an inconsistency between the well-measured expansion history and the growth of structure it predicts. Through a likelihood analysis of current cosmological data that constrain the expansion history, we show that the LCDM upper limits on the expected number of massive, distant clusters are nearly identical to limits predicted by all quintessence models where dark energy is a minimally coupled scalar field with a canonical kinetic term. We provide convenient fitting formulas for the confidence level at which the observation of a cluster of mass M at redshift z can falsify LCDM and quintessence given cosmological parameter uncertainties and sample variance, as well as for the expected number of such clusters in the light cone and the Eddington bias factor that must be applied to observed masses. By our conservative confidence criteria, which equivalently require masses 3 times larger than typically expected in surveys of a few hundred square degrees, none of the presently known clusters falsify these models. Various systematic errors, including uncertainties in the form of the mass function and differences between supernova light curve fitters, typically shift the exclusion curves by less than 10% in mass, making current statistical and systematic uncertainties in cluster mass determination the most critical factor in assessing falsification of LCDM and quintessence.