Speaker
Description
Recent analyses of large-scale galaxy redshift surveys, such as those from Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI), as well as Type Ia supernova data, have made it possible to place meaningful constraints on the dark energy equation of state. Methods based on the Alcock–Paczynski test, which uses the clustering of large-scale structure as a standard shape, baryon acoustic oscillations (BAO) as a standard ruler, and Type Ia supernovae as standard candles all probe the recent expansion history of the Universe. These low-redshift probes consistently indicate that, in the low-redshift Universe ($z<0.8$), the dark energy equation-of-state parameter $w$ does not evolve with time, or evolves only very weakly. This behavior is consistent with that expected from a thawing quintessence field. In contrast, the Planck CMB data favors a dark energy equation of state with a mean value significantly below $w=−1$ at low redshifts and a relatively larger time variation. When adopting cosmological models that include cold dark matter and late-time dark energy, and combining constraints from CMB data with those from low-redshift probes, one obtains a seemingly contradictory result: a recent (z∼0.4) crossing of the phantom divide. If both the observational data and the analysis methods are reliable, this discrepancy between the physical properties of dark energy inferred from high- and low-redshift probes may point to limitations of the assumed cosmological model. Therefore, we extend the paradigm of cosmological models by incorporating the early DE in the current $w^{\rm CPL}$CDM models (or changes in the recombination physics) to see if one can find a model that has late-time expansion history from CMB more consistent with that from low-redshift probes. In particular, with the extended AP test, we investigate whether a unified cosmological model - simultaneously accommodating the Hubble tension through EDE and the low-redshift dark energy behavior - can bring the late-time expansion history inferred from CMB into better agreement with low-redshift probes. Preliminary results and their implications will be presented.