UC Irvine

We present updated constraints on the parameters of an axion dark energy model, for which we took into account the properties of its characteristic potential and its full cosmological evolution. We show that the values of the axion parameters appear sufficiently constrained by the data, including the latest DESI DR1, and are consistent with the theoretical expectations of a field mass ma in the ultralight regime log(mac2/eV)≃-32.60±0.12, and an effective energy scale fa close to the reduced Planck energy log(fa/MPl)≃-0.28±0.19. Our results also support the idea of dynamical dark energy, although Bayesian evidence still favors the phenomenological dark energy model w0wa over the axion dark energy, with the Bayes factor indicating moderate and weak strength of the evidence, respectively, when the models are compared to the cosmological constant Λ. However, the results suggest that axion dark energy remains a well-motivated model and its parameters may be better constrained if the upcoming DESI data show further evidence for dynamical dark energy.