# Null test for interactions in the dark sector

## TL;DR

This paper introduces a null test for interactions in the dark sector based on the evolution of the dark energy and dark matter densities, using model-independent machine learning methods on recent cosmological data.

## Contribution

It proposes a new null test for dark sector interactions and applies machine learning techniques to observational data to assess deviations from standard cosmology.

## Key findings

- Standard $
m extLambda$CDM is consistent within 3σ
- Some deviations at low redshift suggest possible dark sector interactions
- Potential link to H0 tension in cosmology

## Abstract

Since there is no known symmetry in Nature that prevents a non-minimal coupling between the dark energy (DE) and cold dark matter (CDM) components, such a possibility constitutes an alternative to standard cosmology, with its theoretical and observational consequences being of great interest. In this paper we propose a new null test on the standard evolution of the dark sector based on the time dependence of the ratio between the CDM and DE energy densities which, in the standard $\Lambda$CDM scenario, scales necessarily as $a^{-3}$. We use the latest measurements of type Ia supernovae, cosmic chronometers and angular baryonic acoustic oscillations to reconstruct the expansion history using model-independent Machine Learning techniques, namely, the Linear Model formalism and Gaussian Processes. We find that while the standard evolution is consistent with the data at $3\sigma$ level, some deviations from the $\Lambda$CDM model are found at low redshifts, which may be associated with the current tension between local and global determinations of $H_0$.