Speaker
Description
Recent baryon acoustic oscillation and supernova data have stimulated renewed interest in possible departures from the cosmological constant, often interpreted within (w)CDM or (w_0w_a)CDM parametrizations. In particular, redshift-dependent trends in the dark-energy equation of state have been discussed as potential evidence for dynamical dark energy. In this talk, I argue that such an interpretation should be treated with caution.
I will summarize a series of analyses showing that distance-based observables possess intrinsic structural limitations in constraining the time evolution of dark energy. An exact linear-response and Fisher-eigenmode analysis reveals that most of the information carried by distance data is compressed into a small number of geometric modes, while the remaining directions in the dark-energy function space are weakly constrained. As a result, apparent preferences for time-varying dark energy can be sensitive to parametrization choices, matter-density priors, sound-horizon assumptions, and redshift-resolved projection effects.
Using DESI DR2 BAO data, I compare (\Lambda)CDM, (w)CDM, and (w_0w_a)CDM fits, with particular attention to the role of (r_d), the matter-density prior (\Omega_{m0}), and the robustness of the CPL parametrization under basis and prior variations. These studies indicate that the apparent dynamical-dark-energy signal is not yet a model-independent detection of evolving dark energy. Rather, it can arise from the interplay between geometric degeneracies and the limited effective dimensionality of distance probes.
I will also discuss the complementary role of growth observables. While distance probes constrain the integrated expansion history, growth measurements access different physical directions and are therefore essential for testing whether the observed trends correspond to genuine dynamics or to projection artifacts. Taken together, the current evidence remains consistent with (\Lambda)CDM once structural limitations, prior dependence, and cross-probe consistency are properly accounted for.
