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 $H_0=72.0_{-2.1}^{+1.4}$ km/s/Mpc with Union3, without any local $H_0$ prior. These higher values of $H_0$ arise along the ${\Omega }_{\mathrm{m}}$--$H_0$ degeneracy direction while the sound horizon remains nearly unchanged at $r_{\mathrm{d}}\simeq 145$~Mpc, indicating that the enhancement of the late-time expansion rate is a geometrical effect that does not address the early-time calibration of $r_{\mathrm{d}}$. 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 $z\lesssim 0.1$.

arXiv comment9 pages, 8 figures, accepted for publication in MNRAS on 23 September