Testing quintessence axion dark energy with recent cosmological results

Abstract We investigate a quintessence axion model for dynamical dark energy, motivated in part by recent results from the Baryon Acoustic Oscillation (BAO) measurements of the Dark Energy Spectroscopic Instrument (DESI) combined with the cosmic microwave background anisotropies and the latest Type Ia supernovae (SNe Ia) data. By carefully treating the initial conditions and parameter sampling, we identify a preferred parameter space featuring a sub-Planckian axion decay constant and a relatively large axion mass, which naturally avoids the quality problem and remains consistent with the perturbative string conjecture. Our parameter scan also uncovers a trans-Planckian regime of theoretical interest, which is only mildly disfavored even by the strongest constraint. Finally, we discuss the possible connection between this model and the recently reported non-zero rotation of the CMB linear polarization angle, emphasizing the broader cosmological implications and the promising prospects for testing this scenario. We show that an 𝒪(1) electromagnetic anomaly coefficient is preferred by the strongest constraint, which is in full agreement with the minimal quintessence axion model.