Constraints on Redshift-Binned Dark Energy using DESI BAO Data

We parameterize the equation of state of late-time dark energy as w₁₈₍ (z), with three redshift bins, characterized by a constant equation of state in each bin. Then, we constrain the parameters of the w₁₈₍CDM model using datasets from DESI BAO data, Planck CMB power spectrum, ACT DR6 lensing power spectrum, and type Ia supernova distance-redshift data of Pantheon Plus/DES Y5/Union3. The significances for w₁>-1 is 1. 9, 2. 6 and 3. 3, and w₂ is consistent with -1 within 1 level, while 1. 6, 1. 5 and 1. 5 for w₃-1 at 1. 9, 1. 7 and 2. 9 level, meanwhile w₃<-1 at 1. 3, 1. 3 and 1. 3 level, respectively. In all, our results indicate that the transition of dark energy from phantom at high redshifts to quintessence at low redshifts is not conclusive.