A Consistent Approach to Falsifying Lambda-CDM with Rare Galaxy Clusters

Understand

We consider methods with which to answer the question "is any observed galaxy cluster too unusual for Lambda-CDM?" After emphasising that many previous attempts to answer this question will overestimate the confidence level at which Lambda-CDM can be ruled out, we outline a consistent approach to these rare clusters, which allows the question to be answered.

• We define three statistical measures, each of which are sensitive to changes in cluster populations arising from different modifications to the cosmological model.
• We also use these properties to define the 'equivalent mass at redshift zero' for a cluster --- the mass of an equally unusual cluster today.
• This quantity is independent of the observational survey in which the cluster was found, which makes it an ideal proxy for ranking the relative unusualness of clusters detected by different surveys.