The Evolving Story of Dark Energy

The standard model of cosmology, ΛCDM, fixes dark energy to be spatially and temporally constant. Yet a growing set of cosmological observations now strain against this description, suggesting the possibility of time evolution. I have investigated the origins of this preference in data. Galaxy surveys, supernova surveys, and the cosmic microwave background each probe different aspects of the expansion history and show mild but persistent discrepancies in the inferred matter density under ΛCDM. Exploring broader models, this discrepancy can manifest as hints of dynamical dark energy or even an unphysical preference for negative neutrino masses, as shown by my recent works. We traced both effects to a common origin in this matter-density tension, demonstrating that multiple anomalies may arise from the same underlying explanation rather than independent problems to be solved. In parallel, I examined subtle parameter degeneracies that exist within ΛCDM and showed how they may reconcile a portion of these anomalies. Taken together, these results illustrate how a phenomenological approach - mapping observables to the physical parameters and degeneracies they probe can identify where ΛCDM is robust, where it strains, and how these stress points can guide the search for new physics in the dark-energy sector.