Does DESI prefer Damped Oscillating Dark Energy over Cosmological constant?

Abstract

We investigate a dark-energy equation of state governed by a damped harmonic oscillator equation, admitting underdamped, critically damped, and overdamped solutions. Confronting the model with Planck CMB distance priors, DESI BAO, BBN, cosmic chronometers, and three Type Ia supernova compilations, we find that the data select an underdamped solution yielding H0 = 70.9 ± 1.1 $\rm km \ s^{-1} Mpc^{-1}$ with DES-Dovekie and $H_0 = 72.0^{+1.4}_{-2.1}$  $\rm km \ s^{-1} Mpc^{-1}$ with Union3, without any local H0 prior. These higher values of H0 arise along the Ωm–H0 degeneracy direction while the sound horizon remains nearly unchanged at rd ≃ 145 Mpc, indicating that the enhancement of the late-time expansion rate is a geometrical effect that does not address the early-time calibration of rd. In contrast, the Pantheon+ compilation selects a near-critically damped solution with a prior-limited positive w0 and H0 = 66.23 ± 0.85 $\rm km \ s^{-1} Mpc^{-1}$, highlighting the sensitivity of the model to the low-redshift distance information encoded in the different supernova compilations. The Bayesian evidence relative to ΛCDM is inconclusive for the DES-Dovekie and Union3 combinations, whereas Pantheon+ shows a strong preference for the damped-oscillator model, driven by the departure from w = −1 at z ≲ 0.1.