Dark acoustic oscillations as an early-Universe explanation of the DESI anomaly

DESI DR2 data have been widely interpreted as evidence for late-time evolving dark energy (DE) with an apparent phantom crossing. Here we investigate an alternative explanation, based on early-Universe physics. If dark acoustic oscillations (DAOs) are close in scale to baryon acoustic oscillations (BAOs), they can bias the extraction of the BAO scale from the peak in the galaxy correlation function. This leads to an apparent shift in the inferred distance if the superposition of BAO and DAO features is misinterpreted as being due to BAOs only. Taking this shift into account, we find that a DAO with percent-level amplitude can reconcile DESI DR2 with 2018 as well as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>Pantheon</a:mi> <a:mo>+</a:mo> <a:mtext>supernovae</a:mtext> </a:mrow> </a:math> data, with fit improvement at a similar level compared to evolving DE. Notably, a DAO feature with the required properties has been predicted in a previously proposed scenario that resolves the Hubble tension via a prerecombination decoupling of dark matter and dark radiation. The presence of a DAO feature close to the BAO peak can be scrutinized with future full-shape galaxy clustering data from DESI and Euclid.