Abstract: The DESI collaboration (Dark Energy Spectroscopic Instrument) confirmed its groundbreaking results on dynamical dark energy through the largest 3-dimensional Universe map it observed. This talk highlights how DESI Data Release 2 further challenges the ΛCDM paradigm, the standard cosmology for the past 30 years. DESI’s Baryon Acoustic Oscillation (BAO) measurements reveal a 2-4σ preference for dynamical dark energy, particularly when combined with external cosmic microwave background (CMB) data and Supernovae Ia (SNIa) data. Additionally, DESI sets the tightest upper limit on neutrino mass (Σm <0.064eV) under ΛCDM, though the posterior distributions intriguingly favour negative values. The dynamical dark energy model relaxes neutrino mass constraints and leaves open the possibility of inverted mass ordering.
The second part of this talk focuses on the robustness of these cosmological measurements. This includes improved models of the galaxy-dark-matter-halo connection for validating cosmological pipelines and detailed studies of spectroscopic systematics in redshift surveys. These efforts are essential for ensuring precise BAO measurements and reliable constraints on dark energy and neutrino mass.
Bio: Jiaxi Yu is a fellowship postdoc at Kavli IPMU in Japan. Her research interests are observational cosmology, large-scale structure and redshift surveys. Jiaxi obtained her PhD in astrophysics from EPFL in Switzerland under the supervision of Professor Jean-Paul Kneib. She is active in several major international collaborations, including the Dark Energy Spectroscopic Instrument (DESI), the Prime Focus Spectrograph (PFS), and the MUltiplexed Survey Telescope (MUST), with memberships that are portable to institutions outside the collaborations. Her research on the galaxy-dark-matter-halo relation bridges astrophysical modelling and precision cosmology, while her structured work of spectroscopic systematics in emission-line galaxies further enhances the robustness of DESI cosmological results.