Robustness of the intermediate neutrino self-interaction mode

Determine whether the bimodality within the moderately interacting neutrino region, including the weakly interacting and intermediate-interacting branches inferred from DESI DR1 full-shape, BAO, and Lyman-alpha data, persists under alternative treatments of nonlinear evolution and intergalactic-medium physics.

Background

The DESI DR1 analysis including Lyman-alpha data produces two modes within the moderately interacting neutrino region: a weakly interacting branch connected to the standard cosmological model and a narrow intermediate-interacting branch near log10(G_eff MeV^2) approximately equal to -3. The paper emphasizes that Lyman-alpha forest measurements probe nonlinear scales and that their cosmological interpretation depends on modeling nonlinear evolution and intergalactic-medium physics.

Because different Lyman-alpha likelihood constructions, including EFT-based and PRIYA-based treatments, yield different constraints and retain or suppress different interaction modes, the authors leave unresolved whether the intermediate-interacting bimodality is a physical feature or a consequence of the adopted modeling assumptions.