Dark Matter - Dark Energy coupling biasing parameter estimates from CMB data

TL;DR

This paper demonstrates that neglecting dark matter–dark energy coupling in CMB data analysis can lead to significant biases in estimated cosmological parameters, highlighting the importance of considering such couplings.

Contribution

The study shows that assuming no DM-DE coupling when it is present causes biases in key cosmological parameters, emphasizing the need to include coupling as a free parameter.

Findings

Biases in ,c, H0, and ,m occur when coupling is ignored.

No significant bias if no true coupling exists.

Allowing for DM-DE coupling reduces parameter estimation biases.

Abstract

When CMB data are used to derive cosmological parameters, their very choice does matter: some parameter values can be biased if the parameter space does not cover the "true" model. This is a problem, because of the difficulty to parametrize Dark Energy (DE) physics. We test this risk through numerical experiments. We create artificial data for dynamical or coupled DE models and then use MCMC techniques to recover model parameters, by assuming a constant DE state parameter w and no DM--DE coupling. For the DE potential considered, no serious bias arises when coupling is absent. On the contrary, \omega_{o,c}, and thence H_o and \Omega_{o,m}, suffer a serious bias when the "true" cosmology includes even just a mild DM--DE coupling. Until the dark components keep an unknown nature, therefore, it can be important to allow for a degree of freedom accounting for DM--DE coupling, even more than increasing the number of parameters accounting for the w(a) behavior.