DESI Year 1 results:

The Dark Energy Spectroscopic Instrument (DESI) represents the culmination of multi-years efforts and advanced spectroscopic techniques. Placed at Mayall 4-meter Telescope, DESI harnesses the power of 5,000 robotic fiber positioners, coupled with state-of-the-art spectrographs, to capture the spectral signatures of millions of galaxies and quasars with unprecedented precision. DESI success is also based on the collaborative spirit of its community, more than 400 scientists over 72 institutions. DESI started taking data in 2021 and is planned to observe fora total of 5 years.This data release (DESIY1) and the two sets of results announcements on April 14 and November 19 2024 (accompanied by two press releases) correspond to the first year of observations. In terms of cosmological constraints, DESIY1 surpassed the statistical power of 20 years of observations from the 2.5m Apache point Sloan Telescope that gave us the SDSS (2012), BOSS (2015) and e-BOSS (2021) surveys. DESI data provide unprecedented constraints on cosmological parameters, the expansion history of the Universe, the formation and growth of cosmic structures, the properties of dark energy and the properties of neutrinos. Key parts of the analysis pipeline (in particular the blind analysis strategy, algorithm and procedure, and the improved compressed variables approach "ShapeFit") were developed by my research group.DESIY1 has confirmed many aspects of the standard cosmological model, as well as its major shortcomings, in particular the famous Hubble tension. In addition, DESIY1 has shown tantalising hints that the late-time expansion history of the Universe might not match that expected from observations of the early Universe, which can be interpreted as a possible hint of dynamical dark energy, as non-standard neutrino properties or as a new "tension" in the standard cosmological model, although the statistical significance is still too low to draw definitive conclusions. The tree year data are being actively analysed and a new release is expected in spring 2025. The DESIY1 papers will be published in a special issue of the JCAP journal but are already available open access at the link below.