Wandering in the Lyman-alpha forest: a study of dark matter-dark radiation interactions

摘要

The amplitude of large-scale matter uctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave back-ground (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focus-ing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we nd that measurements of the Lyman-alpha ux power spectrum from the Sloan Digital Sky Survey provide no support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of 2Δln Γ = 12 with respect to the standard flcold dark matter (ΛCDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to 2Δln Γ = 6 relative to ΛCDM. We thus con-clude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We nd that the constraint on the e ective number of uid-like dark radiation species, ΔN_(fluid), will be improved by an order of magnitude compared to current bounds.