2025/03/24 by Shota Nakagawa, Nakagawa, Shota, Yuichiro Nakai +5 · 8 citations
Physics and Astronomy · #Particle physics theoretical and experimental studies #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena
paper · pdf · doi:10.48550/arxiv.2503.18924
Recent cosmological observations have revealed growing tensions with the standard ΛCDM model, including indications of isotropic cosmic birefringence and deviations from w = -1 in the dark energy equation of state, as suggested by DESI and supernova measurements. In this paper, we point out that such deviations can arise even from a subdominant energy density component. We then propose a unified framework based on a dynamical axion field that simultaneously accounts for both anomalies, providing a simple and natural extension of the standard ΛCDM model. In our scenario, the axion field with 2H0\lesssim m\lesssim 6H0, where H0 is the current Hubble constant, induces a nonzero rotation of the CMB polarization plane and modifies the present-day dark energy equation of state. This framework accommodates recent observational data with natural parameter choices, even for a string axion with a decay constant of order 1017 GeV.