Dark Energy Crosses the Line: Quantifying and Testing the Evidence for Phantom Crossing

Understand

Combinations of the most recent CMB, BAO, and SNeIa datasets, when analyzed using the CPL parametrization, $w(a) = w_0 + (1 - a) w_a$, exclude $\Lambda$CDM at $\gtrsim\!3\sigma$ in favor of a dark energy equation of state (EoS) parameter that crosses the phantom divide.

• We confirm this behavior and show that it persists when DESI BAO data are replaced by SH0ES $H_0$ measurements, despite the known tension between these probes in the presence of CMB data.
• In both cases, the constraints favor a transition from an early-time phantom-like phase to a late-time quintessence-like phase, with the crossing occurring at different redshifts depending on the dataset combination.
• The probability that a phantom divide line (PDL) crossing does not occur within the expansion history is excluded at significance levels ranging between $3.1\sigma$-$5.2\sigma$.