Fresh look at neutrino self-interactions with the Lyman-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math> forest: Constraints from EFT and PRIYA simulations

We present the first search for evidence of neutrino self-interaction with two new, state-of-the-art likelihoods for eBOSS Lyman-$α$ data. These are an effective field theory (EFT) likelihood with priors from the Sherwood simulation suite, and a compressed likelihood derived from an emulator built using the PRIYA simulation suite. Previous analyses that combined Planck measurements with eBOSS Lyman-$α$ likelihoods based on earlier simulations found a preference for neutrino self-interactions. In contrast, using either of the new eBOSS Lyman-$α$ likelihoods, we find that a joint analysis with the cosmic microwave background (CMB) data from Planck prefers a negligible level of neutrino self-interaction, and derive new constraints on the neutrino self-coupling: $\mathrm{log}_{10}(G_\mathrm{eff} \ \mathrm{MeV}^2)=-5.57_{-0.58}^{+0.98}$ for Planck + EFT Lyman-$α$, and $\mathrm{log}_{10}(G_\mathrm{eff} \ \mathrm{MeV}^2)=-5.16_{-0.67}^{+1.12}$ for Planck + PRIYA Lyman-$α$, at 68% confidence. We also consider Planck in combination with DESI BAO data, and find that the latter does not provide significant constraining power for neutrino self-interactions.