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: log10(GeffMeV2)=−5.57−0.58+0.98 for Planck + EFT Lyman-α, and log10(GeffMeV2)=−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.
@article{arxiv.2503.15592,
title = {Fresh Look at Neutrino Self-Interactions With the Lyman-$\alpha$ Forest: Constraints from EFT and PRIYA Simulations},
author = {Adam He and Mikhail M. Ivanov and Simeon Bird and Rui An and Vera Gluscevic},
journal= {arXiv preprint arXiv:2503.15592},
year = {2025}
}