Primordial high energy neutrinos

TL;DR

This paper explores the potential of detecting primordial high energy neutrinos from the early Universe, analyzing spectral features, constraints, and detection prospects with current and future telescopes.

Contribution

It introduces a comprehensive study of primordial high energy neutrinos, including a new Monte Carlo code for spectrum distortion and an assessment of the primordial origin hypothesis for a specific neutrino event.

Findings

Spectral features of primordial neutrino fluxes identified.

Constraints from BBN and CMB on source particles analyzed.

Monte Carlo code developed for spectrum distortion calculations.

Abstract

Among the few ways to probe the early Universe, neutrinos offer a particular window on high energy phenomena occurring before recombination. We discuss the opportunities of observing primordial high energy neutrinos (Phenus): neutrinos produced before or around recombination from the decay or annihilation of long-lived relics, arriving at detectors today with energies in the GeV-PeV range. We summarise the results of a general study of this scenario, covering the sharp spectral features such fluxes would display, the theoretical (BBN and CMB) and experimental constraints on the source particle parameter space, and the regions that could realistically be probed by current and future neutrino telescopes. We also present a dedicated Monte Carlo code for computing the distortion of the Phenu spectrum by final state radiation and interactions with the cosmic neutrino background during propagation, and apply it to assess the primordial origin hypothesis for the KM3-230213A ultrahigh energy neutrino event.