Accounting for Correlations When Fitting Extra Cosmological Parameters

Understand

Current cosmological tensions motivate investigating extensions to the standard $\Lambda$CDM model.

• Additional model parameters are typically varied one or two at a time, in a series of separate tests.
• The purpose of this paper is to highlight that information is lost by not also examining the correlations between these additional parameters, which arise when their effects on model predictions are similar, even if the parameters are not varied simultaneously.
• We show how these correlations can be quantified with simulations and Markov Chain Monte Carlo (MCMC) methods.