Euclid preparation

Euclid is expected to establish new state-of-the-art constraints on extensions beyond the standard ΛCDM cosmological model by measuring the positions and shapes of billions of galaxies. Specifically, its goal is to shed light on the nature of dark matter and dark energy. Achieving this requires developing and validating advanced statistical tools and theoretical prediction software capable of testing extensions of the ΛCDM model. In this work, we describe how the Euclid likelihood pipeline, Cosmology Likelihood for Observables in Euclid ( CLOE ), has been extended to accommodate alternative cosmological models and to refine the theoretical modelling of Euclid primary probes. In particular, we describe the modifications made to CLOE to incorporate the magnification bias term into the spectroscopic two-point correlation function of galaxy clustering. Additionally, we explain the adaptations made to CLOE ’s implementation of Euclid primary photometric probes to account for massive neutrinos and modified gravity extensions. Finally, we present the validation of these CLOE modifications through dedicated forecasts on synthetic Euclid -like data by sampling the full posterior distribution and comparing with the results drawn from the literature. In conclusion, we have identified several functionalities with regard to beyond-ΛCDM modelling that could be further improved within CLOE . We also outline potential research directions to enhance the pipeline efficiency and flexibility through novel inference and machine learning techniques.

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