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.
One of the fundamental hypotheses in observational cosmology is the validity of the so-called cosmic distance-duality relation (CDDR). In this paper, we perform Monte Carlo simulations based on the method developed in Holanda, Goncalves & Alcaniz (20
12) [JCAP 1206 (2012) 022] to answer the following question: what is the number of galaxy clusters observations N_{crit} needed to check the validity of this relation at a given confidence level? At 2sigma, we find that N_{crit} should be increased at least by a factor of 5 relative to the current sample size if we assume the current observational uncertainty sigma_{obs}. Reducing this latter quantity by a factor of 2, we show that the present number of data would be already enough to check the validity of the CDDR at 2sigma.
