The universe is putting on a show, and the lead role goes to dark energy. For a long time, the actor seemed unchanging: the cosmological constant (the vacuum energy that accelerates cosmic expansion) set the same tone throughout. But new data from the DESI telescope, which measures baryon acoustic oscillations (density waves in the early universe), make us look more closely. Perhaps the actor is changing its mask as the play unfolds.

To understand what is happening, scientists compared several parametrizations of the equation of state (the relation between pressure and energy density). The analysis included DESI DR2 data, three sets of Type Ia supernovae (standard candles for measuring distances), and the cosmic microwave background. The result was unexpected: all dynamical models prefer the Quintom-B scenario, where dark energy crosses the phantom divide. Deviations from the standard model reach 3σ but fall short of the 5σ discovery threshold. Spatial curvature remains compatible with zero, and the upper limit on the sum of neutrino masses (light elementary particles that affect structure) for ΛCDM is <0.066 eV.

Previously, it was unclear whether DESI DR2 truly demands abandoning the cosmological constant and how much the conclusions depend on the choice of model and the treatment of neutrinos. Now it has been shown that dynamical models, especially Quintom-B, are preferred over ΛCDM at up to 3σ, but none reaches 5σ. Upper limits on the sum of neutrino masses were obtained, which depend strongly on the dark energy model. This means that interpreting future data will require caution.

If the deviations are confirmed as DESI and other surveys improve in precision, the standard model will have to be revised. Possible avenues include scalar fields, modified gravity, or interactions between dark components. The results are important for planning future missions such as Euclid and Roman, and for refining neutrino mass limits in cosmology. The show goes on, and the actor seems to be preparing a new entrance.