Is Dynamical Dark Energy Necessary? DESI BAO and Modified Recombination

Understand

Recent measurements of baryon acoustic oscillations (BAO) by the Dark Energy Spectroscopic Instrument (DESI) exhibit a mild-to-moderate tension with cosmic microwave background (CMB) and Type Ia supernova (SN) observations when interpreted within the $\Lambda$CDM framework.

• This discrepancy has been cited as evidence for dynamical dark energy (DDE).
• Given the profound implications of DDE for fundamental physics, we explore whether the tension can instead be resolved by modifying the physics of recombination.
• We find that a phenomenological model of modified recombination can effectively reconcile the BAO and CMB datasets and, unlike DDE, also predicts a higher Hubble constant $H_0$, thereby partially alleviating the Hubble tension.