IceCube's diffuse neutrino flux tightens limits on neutrino disappearance

Even without knowing where astrophysical neutrinos come from or at what redshift they were produced, the observed diffuse flux at IceCube places tight limits on any process that exponentially attenuates neutrinos in transit — including invisible decay and interactions with cosmic backgrounds. A fit to IceCube's High-Energy Starting Events constrains these attenuation effects across a range of assumptions about source distributions and energy dependence. A useful side finding: allowing even the weakly constrained level of energy-dependent attenuation can shift the inferred spectral index of the diffuse flux, with implications for source modeling.