Project

Distorted by the gravity of cosmic structures, galaxy shapes can answer the biggest questions in cosmology: What are dark matter and dark energy? How do cosmic structures form?

The standard cosmological model can explain many observations, but it relies on two components we still do not understand: dark matter and dark energy. To investigate their nature, the Euclid mission and the Vera Rubin Observatory will measure the shapes of billions of galaxies, which are slightly distorted by the gravity of cosmic structures, an effect known as weak lensing. Fully realising the potential of these datasets will require highly precise data analysis techniques.

OCAPi develops new data analysis methods to optimally extract cosmological information from weak lensing observations and applies them to Euclid data. While standard analyses compress the data and lose information, OCAPi analyses lensing maps pixel by pixel, directly comparing observations with simulations of the Universe within a Bayesian framework. This approach captures the full information content of the data, maximising precision and improving our ability to distinguish cosmological signals from systematic effects.

By analysing the data at the field level, OCAPi simultaneously constrains cosmological parameters and reconstructs the matter distribution in the Universe. This pixel-level approach enables direct comparison between theory and observations and improves the precision of cosmological constraints. OCAPi also delivers probabilistic maps of the matter distribution across cosmic times, effectively making dark matter visible and opening new ways to test physics with cosmic structures.

By maximising the scientific return of Euclid’s weak lensing data, OCAPi will advance our understanding of dark matter and dark energy, and deliver a “digital twin” of the Universe.