Abstract
Do neutrinos have sizable self-interactions? They might. Laboratory constraints are weak, so strong effects are possible in astrophysical environments and the early universe. Observations with neutrino telescopes can provide an independent probe of neutrino self ("secret") interactions, as the sources are distant and the cosmic neutrino background intervenes. We define a roadmap for making decisive progress on testing secret neutrino interactions governed by a light mediator. This progress will be enabled by IceCube-Gen2 observations of high-energy astrophysical neutrinos. Critical to this is our comprehensive treatment of the theory, taking into account previously neglected or overly approximated effects, as well as including realistic detection physics. We show that IceCube-Gen2 can realize the full potential of neutrino astronomy for testing neutrino self-interactions, being sensitive to cosmologically relevant interaction models. To facilitate forthcoming studies, we release nuSIProp, a code that can also be used to study neutrino self-interactions from a variety of sources.
Highlights
We return to our opening question: Do neutrinos have sizable self-interactions? In the laboratory, this is impossible to answer through scattering and is not adequately constrained through particle decays
This question is of central importance to particle theory, as neutrinos allow unique tests of new physics
It is of central importance to cosmology, as allowed νSI parameters would indicate the presence of strong self-scattering in the early Universe
Summary
Laboratory limits, mostly from mesondecay experiments, are relatively weak [5], allowing νSI to have large effects, potentially explaining short baseline neutrino anomalies [6–12] and the muon g − 2 anomaly [13–17]. Allowed νSI would dramatically affect the evolution of systems with high neutrino densities, such as supernovae [18] and the early Universe [4,19–22]. This is why large cosmological effects from νSI remain allowed. A new opportunity to probe νSI has arisen [40–42] due to the detection of high-energy neutrinos by IceCube. Ντ self-interactions are the least explored, leaving room for significant cosmological neutrino effects. A combination of observables can fully probe the range of νSI that would significantly affect the dynamics of the cosmic neutrino background. In Appendix, we give the results of the full νSI cross-section calculation
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