Speaker
Description
Recent BAO observations from the DESI collaboration, combined with CMB and supernovae data, suggest a preference for evolving dark energy (DE) in place of a cosmological constant, particularly within the widely used CPL parameterization of the DE equation of state. In this talk, I present an alternative and complementary approach that instead describes the evolution of the DE density directly, using two physically transparent parameters — one capturing how much DE density differs from today's value at a well-chosen reference epoch, and the other capturing how fast it is changing at that same epoch. This formulation avoids technical degeneracies that affect the standard CPL approach, and each of its two parameters is tightly measured by a distinct subset of the data: namely the DE density fraction relative to today at the reference epoch is pinned down by supernovae, while its rate of change by the combination of BAO and CMB. Applied to the latest DESI, CMB, and supernova data, both parameters are found to be measured to percent level precision, with their mean values interestingly close to the expectation for a cosmological constant, and the overall preference for evolving DE remaining below the three-sigma level. These findings urge caution in interpreting current hints of dynamical DE and highlight the importance of how we choose to describe it.