Exotic Dark Matter and the DESI Anomaly

Understand

Exotic dark matter (EDM) refers to a dark matter species whose equation of state deviates from zero at late times.

• This behavior enables it to model a variety of non-standard late-time cosmologies, offering alternatives to various dark energy (DE) models, especially when the DE sector violates the null energy condition.
• In this work, by fitting to CMB, BAO, and Supernovae (SNe) data and comparing models in a Bayesian approach, we show that simple models of exotic dark matter are statistically comparable to the $w_0w_a$CDM DE model in explaining the recent anomaly in the late-time cosmological evolution suggested by DESI and supernova observations, although in both classes of models the evidence against the $\Lambda$CDM model only appears when the DES-Y5 or Union3 SNe dataset is included.
• The value of $H_0$ remains similar to that in the DE model, except in the no-SNe case, where the DE model predicts lower values than $\Lambda$CDM, thereby worsening the Hubble tension, whereas the EDM models yield values closer to that of $\Lambda$CDM, albeit with larger uncertainty.