Speaker
Description
Baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) strengthen the cosmological evidence for dark energy beyond the cosmological constant to the ~3σ level when combined with cosmic microwave background (CMB) and Type Ia supernovae (SNe Ia) observations. This evidence is obtained assuming a dark energy equation of state restricted to linear order in the scale factor, and an active area of research is determining how this restriction affects the data’s preferences. Dark energy “reconstructions” take a data-driven approach, describing dark energy’s properties with flexible functions that have fewer restrictions on the possible forms of evolution. We parametrize the dark energy equation of state and energy density using piecewise constant functions of redshift, effectively inferring these functions’ averages within seven redshift bins from $z=0$ to $z=4.2$. Across six different BAO and SNe Ia dataset combinations—with BAO from DESI and the Sloan Digital Sky Survey (SDSS) alongside the latest, recalibrated SNe Ia samples—we find local deviations from $\Lambda$CDM with significance up to ~3σ in the energy density and ~2σ in the equation of state. Our results are broadly consistent with linear evolution and indicate a tentative phantom crossing, most clearly manifesting as a local maximum in the dark energy density.