Mini-Symposium: Dark Energy and the Early Universe: the Lilienfeld Prize Session

The local Hubble expansion rate measured using the Cepheid distance ladder by the SH0ES collaboration, the observed anomaly in the baryon acoustic oscillation (BAO) feature evolution from the DESI collaboration, and the S₈ tension—representing anomalous growth of structure—may all signal the emergence of new phases of dark energy dominance, unconventional evolution of dark energy, or extra contributions to the energy and matter density of the Universe from relativistic species or extra neutrinos. Our analyses show that the high-significance dark energy evolution indicated by combined DESI BAO and Type Ia supernova data remains robust, even with new parameterizations, including the transitional dark energy (TDE) model, which posits an abrupt shift in the dark energy equation of state. In related work, we find that a cosmology with a thermalized extra, eV-scale sterile neutrino is as consistent with the Hubble tension data as ΛCDM. The high-precision measurements of expansion and structure growth from current surveys suggest either transitions in dark energy evolution or more complicated expansion and growth histories that may require more complex models. We present frameworks to test these findings' potential indication of beyond ΛCDM cosmology as additional, higher precision data becomes available.