Exotic Dark Matter and the DESI Anomaly

TL;DR

This paper investigates exotic dark matter models that deviate from standard assumptions, showing they can explain recent cosmological anomalies and offer alternative insights into the universe's energy composition and the Hubble tension.

Contribution

It introduces and tests simple exotic dark matter models against observational data, demonstrating their statistical viability and potential to address the DESI anomaly and coincidence problem.

Findings

EDM models are statistically comparable to $w_0w_a$CDM in explaining the DESI anomaly.

EDM models predict a different present-day energy budget compared to standard cosmology.

EDM models yield $H_0$ values closer to $ ext{Lambda}$CDM}$, reducing the Hubble tension.

Abstract

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. In addition, the EDM models predict a drastically different energy budget for the present-day universe compared to the standard model, and provide an explanation for a coincidence problem in the DE-model explanation of the DESI anomaly.