# Neutrino Echoes from Multimessenger Transient Sources

## TL;DR

This paper proposes using time delay signatures in neutrino signals caused by secret interactions with cosmic backgrounds as a new way to test physics beyond the Standard Model, leveraging future multimessenger observations.

## Contribution

It introduces a novel method of probing neutrino interactions beyond the Standard Model through neutrino echoes in multimessenger astrophysics.

## Key findings

- Neutrino echoes can serve as probes of BSM neutrino interactions.
- Future experiments like IceCube-Gen2 can detect these signatures.
- Constraints from this method complement existing laboratory tests.

## Abstract

The detection of the high-energy neutrino event, IceCube-170922A, demonstrated that multimessenger particle astrophysics triggered by neutrino alerts is feasible. We consider time delay signatures caused by secret neutrino interactions with the cosmic neutrino background and dark matter and suggest that these can be used as a novel probe of neutrino interactions beyond the Standard Model (BSM). The tests with BSM-induced neutrino echoes are distinct from existing constraints from the spectral modification and will be enabled by multimessenger observations of bright neutrino transients with future experiments such as IceCube-Gen2, KM3Net, and Hyper-Kamiokande. The constraints are complementary to those from accelerator and laboratory experiments and powerful for testing various particle models that explain tensions prevailing in the cosmological data.