Science Project

The concordance model of cosmology has been very successful at explaining a wide range of observations with only a few
parameters. However, the nature of the main components (dark energy, dark matter, inflation) are still unknown. In addition, with
the increasing quality of cosmological data, tensions such as the Hubble and the S8 tensions have arisen. It is now more important
than ever to question the underlying hypotheses of the concordance model.
One of them relies on the assumption that the primordial power spectrum (hereafter PPS, the distribution of fluctuations at the end
of the inflation era) is derived from simple smooth inflationary potentials and thus close to scale invariant. However, some
cosmological scenarios predict more complex shapes of the PPS. Primordial fluctuations evolve to give rise to the cosmological
structures we see today, but evolve differently depending on the overall cosmological model (content of the Universe, age of the
Universe, time and duration of the epoch of reionisation, …). The potential features present in the PPS will show as new features
in the later time observations, but unfortunately, the latter may also contain features produced during the evolution of the Universe.
It is thus necessary to combine probes of the structuration of the universe at different epochs to break the degeneracies between
PPS shape and late time evolution. This is the goal of this project, which will take advantage of the complementary expertise of the
two teams, to retrieve the shape of the PPS by combining early time probes like the Cosmic Microwave Background (CMB)
anisotropies and late time probes such as Galaxy Clusters (GC), and thus test the robustness of the cosmological parameter
estimations and potentially solve the tensions.