A low-$z$ test for interacting dark energy

TL;DR

This paper proposes a low-redshift observational test using galaxy cluster gas mass fractions to detect potential interactions between dark matter and dark energy, aiming to address the coincidence problem.

Contribution

It introduces a novel low-$z$ test applicable to interacting dark energy models and assesses observational requirements through current data and simulations.

Findings

Current data insufficient to detect interaction

Reducing measurement errors is more effective than increasing sample size

Forecasts specify observational improvements needed for detection

Abstract

A non-minimal coupling between the dark matter and dark energy components may offer a way of solving the so-called coincidence problem. In this paper we propose a low-$z$ test for such hypothesis using measurements of the gas mass fraction $f_{\rm{gas}}$ in relaxed and massive galaxy clusters. The test applies to any model whose dilution of dark matter is modified with respect to the standard $a^{-3}$ scaling, as usual in interacting models, where $a$ is the cosmological scale factor. We apply the test to current $f_{\rm{gas}}$ data and perform Monte Carlo simulations to forecast the necessary improvements in number and accuracy of upcoming observations to detect a possible interaction in the cosmological dark sector. Our results show that improvements in the present relative error $\sigma_{\rm{gas}}/f_{\rm{gas}}$ are more effective to achieve this goal than an increase in the size of the $f_{\rm{gas}}$ sample.