Dark Acoustic Oscillations and the Hubble Tension

Abstract

The Hubble tension and the recently reported anomaly in data from the Dark Energy Spectroscopic Instrument (DESI) are considered to pose serious challenges to the standard $Λ$CDM model of cosmology. In this work, we show that resolving the Hubble tension with a scenario featuring dark radiation-matter decoupling (DRMD) predicts the presence of dark acoustic oscillations (DAO) similar in scale to baryon acoustic oscillations (BAO). Using an inference independent of large-scale structure data, relying only on Planck measurements of the cosmic microwave background and SH$0$ES-calibrated supernova data, we find evidence for a DAO signal with drag-horizon scale $r_{d,\mathrm{DAO}} \in[54,65]\,\mathrm{Mpc}/h$ ($68\%\,\mathrm{C.I.}$) and amplitude $A_\mathrm{DAO} \in [0.02,0.05]$ ($68\%\,\mathrm{C.I.}$). These predictions provide a concrete target for current and upcoming large-scale structure surveys, including DESI, Euclid, and the Roman Space Telescope. Remarkably, the predicted DAO properties are consistent with those required to explain the DESI anomaly, offering both an alternative to evolving dark energy and a preliminary validation of the relevance of a dark radiation-matter decoupling scenario for addressing the Hubble tension.

Figures (4)

• Figure 1: 1D posterior of the dark drag horizon, $r_{d,\mathrm{DAO}}$, from CMB alone (Planck 2018 temperature, polarization, and lensing) and from CMB combined with calibrated supernovae (Pantheon+ and SH$0$ES prior on the absolute magnitude $M$). Also shown are the corresponding posteriors from the four-parameter DRMD analysis of Ref. Garny:2025kqj (including DESI DR2) and the DAO bias study of Ref. Garny:2025szk. All curves are normalized to the same integral over the plotted interval. The compatibility of all curves with a value around $60\, \mathrm{Mpc}/h$ is one of the main results of this work. For reference, the baryon drag horizon is centred around $100\, \mathrm{Mpc}/h$.
• Figure 2: CMB temperature anisotropies for the global best-fit obtained from our combined analysis with CMB and SH$0$ES-calibrated supernova data. We compare DRMD with DAO ($f_\mathrm{idm}>0$, blue) and without DAO ($f_\mathrm{idm}=0$, red dashed). The lower panels show the relative difference. Left: In harmonic space, the DAO imprint percent-level oscillatory features in the temperature power spectrum $C_\ell^\mathrm{TT}$, together with a broadband suppression induced by enhanced decay of the gravitational potential. Planck residuals are shown as gray error bars. We note the change in spacing of the axes as separated by the vertical line at $\ell=30$. Right: In position space, this imprint appears as a localized feature in the angular correlation function $C(\theta)$ (blue-shaded band) at the permille level. The coloured dashed lines correspond to different choices of the DAO drag horizon scale.
• Figure 3: BAO-DAO decomposition of the linear matter power spectrum $P_\text{lin}(k)$ (left) and corresponding correlation function $\xi(r)$ (right) for the global best-fit obtained from our combined analysis with CMB and SH$0$ES-calibrated supernova data. The lower panels show the DAO (blue) and BAO (green) features relative to the smooth broadband contribution (dotted lines in the upper panels). For details on the decomposition into smooth and wiggly BAO as well as DAO contributions, see section \ref{['results']}.
• Figure 4: Marginalized 2D posterior from our analysis using CMB data (black) and CMB combined with calibrated supernova (purple dashed). The inner and outer contours correspond to the 68% and 95% confidence levels. Left: The SH$0$ES determination of $H_0$ is shown as the gray band Riess:2021jrx. Within DRMD, Planck 2018 becomes fully consistent with SH$0$ES. Marginalization over $r_{d,\mathrm{DAO}}$ induces strong projection effects due to parameter degeneracies, which are largely broken by including calibrated supernova data. Right: Targets for future searches: DRMD predicts a percent-level DAO amplitude at dark drag horizon scales of approximately $60\, \mathrm{Mpc}/h$.