The precise determination of cosmological parameters, including the properties of dark energy, are at the heart of the Planck and Euclid space missions. They are also those of major ground-based telescope survey projects with very similar methodological approaches: DES, Vera Rubin, DESI. The ultimate constraints will be obtained by the joint use of data sets from these different experiments. However, this objective requires a complex step: these data sets are indeed from partially overlapping sky areas. This requires on the one hand to take into account the effect of redundancy of data from different instruments, thus whose selection effects are radically different, an advantage to identify spurious systematics errors, but also, on the other hand, to take into account the fact that the overlap of these data brings additional information through their cross-correlation, The joint use of these data therefore requires the development of appropriate methods, which is the case for the joint use of future Euclid data with Planck data, but which has not yet been taken into account for the joint use with other data that are already available or that will be available in the next few years or even months.
The purpose of the IRN is primary to identify the best strategies on short term and facilitate their implementation, but also to design appropriate strategies for the future.
The IRN (International research network ) is supported by INSU-CNRS.
