Dark sectors with mass thresholds face cosmological datasets
Itamar J. Allali, Fabrizio Rompineve, Mark P. Hertzberg
Abstract
Interacting dark sectors may undergo changes in the number of their relativistic species during the early universe, due to a mass threshold $m$ (similar to changes in the Standard Model bath), and in doing so affect the cosmic history. When such changes occur close to recombination, i.e., for $m\ensuremath{\sim}(0.1--10)\text{ }\text{ }\mathrm{eV}$, the stringent bound on the effective number of neutrino species, ${N}_{\mathrm{eff}}$, can be relaxed and the value of the Hubble expansion rate ${H}_{0}$ inferred from cosmic microwave background (CMB) observations raised. We search for such sectors (with and without mass thresholds) in the latest cosmological datasets, including the full-shape (FS) of BOSS DR12 galaxy power spectrum. We perform a detailed analysis, accounting for the choice of prior boundaries and additionally exploring the possible effects of dark sector interactions with (a fraction of) the dark matter. We find $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}\ensuremath{\le}0.55(0.46)$ at 95% confidence level (CL) with (without) a mass threshold. While a significantly larger Hubble rate is achieved in this scenario, ${H}_{0}=69.0{1}_{\ensuremath{-}1.1}^{+0.66}$, the overall fit to $\mathrm{CMB}+\mathrm{FS}$ data does not provide a compelling advantage over the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Furthermore, we find that dark matter interactions with the dark sector do not significantly improve the (matter fluctuations) ${S}_{8}$ tension with respect to the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model. Our work provides model-independent constraints on (decoupled) dark sectors with mass thresholds around the eV scale.