Special IPAC Seminar by Dr. Yun Wang (Caltech/IPAC): "Model-Independent Measurement of Dark Energy from DESI DR2 Data"

Using DESI DR2 baryon acoustic oscillation distance measurements and Planck cosmic microwave background distance priors, we have measured the dark energy density ρX(z) and dark energy equation of state wX(z) as free functions of redshift (smoothly interpolated from values at z=0,1/3,2/3,1,4/3,2.33), and find both to be consistent with a cosmological constant, with only deviations of 1.2σ for ρX(z) and 1.9σ for wX(z) at z=2/3. Our results differ noticeably from those of the DESI Collaboration, in which they used the same DESI DR2 data combined with Planck data and found a 3.1σ deviation from a cosmological constant, a finding which is the consequence of their assuming the parametrization wX(z)=w0+wa(1−a). Our results indicate that assuming a linear wX(z) could be misleading and precludes discovering how dark energy actually varies with time at higher redshifts. In our quest to discover the physical nature of dark energy, the most urgent goal at present is to determine definitively whether dark energy density varies with time. We have demonstrated that it is of critical importance to measure dark energy density as a free function of redshift from data. I will discuss our results, and the important roles for space missions Roman and Euclid in advancing our understanding of dark energy.