Modified gravity interpretation of the evolving dark energy in light of DESI data

The Dark Energy Spectroscopic Instrument (DESI) collaboration has recently released measurements of baryon acoustic oscillation (BAO) from the first year of observations. A joint analysis of DESI BAO, cosmic microwave background (CMB), and Type Ia supernovae (SNe Ia) probes indicates a preference for time-evolving dark energy. We evaluate the robustness of this preference by replacing the DESI distance measurements at z<0. 8 with the Sloan Digital Sky Survey (SDSS) BAO measurements in a similar redshift range. Assuming the w₀w₀CDM model, we find an evolution of the dark energy equation of state parameters consistent with. Our analysis of ^2 statistics across various BAO datasets shows that DESI's preference for evolving dark energy is primarily driven by the two luminous red galaxy (LRG) samples at z₄₅₅=0. 51 and z₄₅₅=0. 71, with the latter having the most significant impact. Taking this preference seriously, we study a general Horndeski scalar-tensor theory, which provides a physical mechanism to safely cross the phantom divide, w=-1. Utilizing the effective field theory of dark energy and adopting the w₀w₀CDM background cosmological model, we derive constraints on the parameters w₀=-0. 8560. 062 and w₀=-0. 53-₀. ₂₆^+0. 28 at 68% CL from Planck CMB, Planck and Atacama Cosmology Telescope (ACT) CMB lensing, DESI BAO, and Pantheon+datasets, showing good consistency with the standard w₀w₀CDM model. The modified gravity model gives results discrepant with at the 2. 4 level, while for w₀w₀CDM it is at 2. 5, based on the best-fit ^2 values. We conclude that modified gravity offers a viable physical explanation for DESI's preference for evolving dark energy.