Papers › Discovering a new well: Decaying dark matter with profile likelihoods
Discovering a new well: Decaying dark matter with profile likelihoods
Emil Brinch Holm, Laura Herold, Steen Hannestad, Andreas Nygaard, Thomas Tram
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A large number of studies, all using Bayesian parameter inference from Markov Chain Monte Carlo methods, have constrained the presence of a decaying dark matter component. All such studies find a strong preference for either very long-lived or very short-lived dark matter. However, in this letter, we demonstrate that this preference is due to parameter volume effects that drive the model towards the standard ΛCDM model, which is known to provide a good fit to most observational data. Using profile likelihoods, which are free from volume effects, we instead find that the best-fitting parameters are associated with an intermediate regime where around 3 % of cold dark matter decays just prior to recombination. With two additional parameters, the model yields an overall preference over the ΛCDM model of Δχ² ≈-2.8 with \textit{Planck} and BAO and Δχ² ≈-7.8 with the SH0ES H₀ measurement, while only slightly alleviating the H₀ tension. Ultimately, our results reveal that decaying dark matter is more viable than previously assumed, and illustrate the dangers of relying exclusively on Bayesian parameter inference when analysing extensions to the ΛCDM model.
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