Papers › Comprehensive Constraints on Dark Radiation Injection After BBN
Comprehensive Constraints on Dark Radiation Injection After BBN
Alexander C. Sobotka, Adrienne L. Erickcek, Tristan L. Smith
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We derive constraints on the injection of free-streaming dark radiation after big bang nucleosynthesis (BBN) by considering the decay of a massive hidden sector particle into dark radiation. Such a scenario has the potential to alleviate the Hubble tension by introducing a new energy component to the evolution of the early universe. We employ observations of the cosmic microwave background (CMB) from Planck 2018 and the South Pole Telescope (SPT-3G), measurements of the primordial deuterium abundance, Pantheon+ Type Ia supernovae data, and baryon acoustic oscillation (BAO) measurements from BOSS DR12 to constrain these decay scenarios. Pre-recombination decays are primarily restricted by observations of the CMB via their impact on the effective number of relativistic species. On the other hand, long-lived decay scenarios in which the massive particle lifetime extends past recombination tend to decrease the late-time matter density inferred from the CMB and are thus subject to constraints from Pantheon+ and BAO. We find that, when marginalizing over lifetimes of τ_Y = [10^(-12.08), 10^(-1.49)] Gyr, the decaying particle is limited at 2σ to only contribute a maximum of 3% of the energy density of the universe. With limits on these decays being so stringent, neither short-lived nor long-lived scenarios are successful at substantially mitigating the Hubble tension.
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