Dark sectors with mass thresholds face cosmological datasets

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 (0. 1--10) eV, the stringent bound on the effective number of neutrino species, N₄₅₅, can be relaxed and the value of the Hubble expansion rate H₀ 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 N₄₅₅0. 55 (0. 46) at 95% confidence level (CL) with (without) a mass threshold. While a significantly larger Hubble rate is achieved in this scenario, H₀=69. 01-₁. ₁^+0. 66, the overall fit to CMB+FS data does not provide a compelling advantage over the model. Furthermore, we find that dark matter interactions with the dark sector do not significantly improve the (matter fluctuations) S₈ tension with respect to the model. Our work provides model-independent constraints on (decoupled) dark sectors with mass thresholds around the eV scale.