InDark focuses on investigating crucial aspects of the standard cosmological model and its extensions, and their connection with particle physics. This includes models of inflation in the early Universe, the nature of dark matter and dark energy, the properties of neutrinos and other light relics, and the viability of modified gravity models. 

 

In the past two decades, we have witnessed tremendous progress in cosmology, thanks to the wealth of data that have become available from experiments like Planck, that released its legacy data in 2018, the many multi-wavelength surveys that mapped the large-scale structure of the Universe to unprecedented precision, like SDSS-BOSS, and a number of probes of cosmic expansion, such as that provided by SN-Ia. This has allowed sharpening our understanding of the Universe. Even though most of the data can be interpreted in terms of the concordance Lambda-Cold Dark Matter (ΛCDM) model, recently some tensions between different observations have surfaced that might point to the necessity of revising the model. Moreover, even if phenomenologically very successful, the ΛCDM is somehow unsatisfying from the point of view of fundamental physics, as the very nature of dark energy and dark matter, as well as the details of the early phase of inflationary expansion, are still unknown. Indeed, these two open issues – observational tensions and theoretical understanding of the model – might well be related.  Coming years will bring an ever-increasing amount of new data, from the next generation of cosmic microwave background (CMB) polarization experiments, aiming at the detection of B-modes, both primordial and lensing-generated (e.g. Simons Observatory, LiteBIRD, CMB-S4), to the galaxy and galaxy cluster surveys from the next large-scale structure (LSS) probes (e.g. Euclid, DESI, SKA, WFIRST, LSST). Gravitational waves (GW) observatories like the operating VIRGO and LIGO, and in the future LISA and the Einstein Telescope, are sensitive to early Universe signals and can act as laboratories to test fundamental physics, other than being able to constrain the expansion history of the Universe through the observations of standard sirens. This wealth of data will have to be interpreted in light of models.

Within InDark, we interpret the combined information from present and future observations of CMB radiation, LSS, GW signals, and other cosmological probes in light of models, while also sharpening the theoretical tools that allow such an interpretation. To this purpose, we employ a wide range of techniques, including theoretical modelling of the cosmological evolution (using both analytical and numerical methods), analysis and interpretation of available data, simulations of mock data samples from future experiments. Our goal is to advance in the path that goes from a simple phenomenological description of the Universe and of its evolution, to fully understanding the nature of its constituents, the behaviour of gravity on cosmological scales and the mechanisms generating the primordial cosmological perturbations. At the same time, this strategy allows to constrain models of particle physics. Once paired with reliable theoretical predictions, present and forthcoming data provide a treasure trove that allows to test with increasing accuracy, and possibly rule out, various models of the Universe, its evolution and the structures within.