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 $H_0 = 70.9 \pm 1.1$ km/s/Mpc with DES-Dovekie and $H_0 = 72.0^{+1.4}_{-2.1}$ km/s/Mpc with Union3, without any local $H_0$ prior. These higher values of $H_0$ arise along the $\Omega_{\rm m}$--$H_0$ degeneracy direction while the sound horizon remains nearly unchanged at $r_{\rm d} \simeq 145$~Mpc, indicating that the enhancement of the late-time expansion rate is a geometrical effect that does not address the early-time calibration of $r_{\rm d}$. In contrast, the Pantheon+ compilation selects a near-critically damped solution with a prior-limited positive $w_0$ and $H_0 = 66.23 \pm 0.85$ km/s/Mpc, highlighting the sensitivity of the model to the low-redshift distance information encoded in the different supernova compilations. The Bayesian evidence relative to $\Lambda$CDM 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 $z\lesssim0.1$.