Indications of a late-time interaction in the dark sector

TL;DR

This paper provides evidence that a late-time interaction between dark matter and vacuum energy is favored by current cosmological data, suggesting modifications to the standard Lambda Cold Dark Matter model.

Contribution

It introduces a parameterized model of dark sector interaction across redshift bins and demonstrates its compatibility with multiple datasets, showing evidence for late-time interaction.

Findings

Non-zero late-time interaction is very likely according to data.

Moderate Bayesian evidence supports interaction starting at redshift 0.9.

Null interaction (Lambda CDM) is excluded at 99% confidence level.

Abstract

We show that a general late-time interaction between cold dark matter and vacuum energy is favoured by current cosmological datasets. We characterize the strength of the coupling by a dimensionless parameter $q_V$ that is free to take different values in four redshift bins from the primordial epoch up to today. This interacting scenario is in agreement with measurements of cosmic microwave background temperature anisotropies from the Planck satellite, supernovae Ia from Union 2.1 and redshift space distortions from a number of surveys, as well as with combinations of these different datasets. We show that a non-zero interaction is very likely at late times. We then focus on the case $q_V\not=0$ in a single low-redshift bin, obtaining a nested one parameter extension of the standard $\Lambda$CDM model. We study the Bayesian evidence, with respect to $\Lambda$CDM, of this late-time interaction model, finding moderate evidence for an interaction starting at $z=0.9$, dependent upon the prior range chosen for the interaction strength parameter $q_V$. For this case the null interaction ($q_V=0$, i.e.$\Lambda$CDM) is excluded at 99% c.l..