Dark Acoustic Oscillations as an Early-Universe Explanation of the DESI Anomaly

TL;DR

This paper proposes that dark acoustic oscillations in the early universe could explain the DESI anomaly, offering an alternative to late-time dark energy models and aligning with Planck and supernova data.

Contribution

It introduces the idea that early-Universe dark acoustic oscillations can bias BAO measurements, providing a novel explanation for the DESI anomaly consistent with existing cosmological data.

Findings

DAO can reconcile DESI DR2 with Planck 2018 data.

A DAO with percent-level amplitude is sufficient to explain the anomaly.

Future galaxy clustering data can test the DAO hypothesis.

Abstract

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 (DAO) are close in scale to baryon acoustic oscillations (BAO), 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 BAO only. Taking this shift into account, we find that a DAO with percent-level amplitude can reconcile DESI DR2 with Planck 2018 as well as Pantheon+ supernovae data, with fit improvement at a similar level as 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 pre-recombination decoupling of dark matter and dark radiation (DRMD). 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.