Ultra-high energy neutrino fluxes: new constraints and implications

Abstract

We apply new upper limits on neutrino fluxes and the diffuse extragalactic component of the GeV γ−ray flux to various scenarios for ultra high energy cosmic rays and neutrinos. As a result we find that extra-galactic top-down sources can not contribute significantly to the observed flux of highest energy cosmic rays. The Z-burst mechanism where ultra-high energy neutrinos produce cosmic rays via interactions with relic neutrinos is practically ruled out if cosmological limits on neutrino mass and clustering apply.

Extragalactic propagation of ultrahigh energy cosmic-rays

“…Above 10 19 eV the universe becomes more and more transparent to photons and very high energy gamma rays can propagate a few tens of megaparsecs without losing a large amount of energy. As a result, these very high energy cosmogenic gamma-rays were discussed in the literature either as signatures of the so called Top-Down models (see for instance [166,167,168,169]) or as probes of UHECR acceleration in the local universe (e.g, [170,166,167,169,171,172,173,174,175,176,177,165]). Since electromagnetic cascades, piling up below 100 GeV, are produced during UHECR propagation and are likely to be associated with the production of cosmogenic neutrinos, it has been soon realized that measurements of the diffuse gamma-ray background could allow to put constraints on the cosmological evolution of the UHECR luminosity [23] and on the maximum allowable cosmogenic neutrino fluxes [178].…”

“…Since electromagnetic cascades, piling up below 100 GeV, are produced during UHECR propagation and are likely to be associated with the production of cosmogenic neutrinos, it has been soon realized that measurements of the diffuse gamma-ray background could allow to put constraints on the cosmological evolution of the UHECR luminosity [23] and on the maximum allowable cosmogenic neutrino fluxes [178]. Modern versions of these calculations were attempted using the EGRET measurements [179,180] in [155,169,181]. More recently, the Fermi satellite measurements [182] reported a gamma-ray background between 100 MeV and 100 GeV lower than previously estimated using EGRET data.…”

Prospects for the Giant Metrewave Radio Telescope to observe radio waves from ultra high energy particles interacting with the Moon

“…As a benchmark scenario, we indicate in Fig. 9 the predicted flux from one TD model [28] where the mass scale resides around 10 22 eV.…”

Cosmic neutrinos from the sources of galactic and extragalactic cosmic rays

“…In topdown models it is assumed that the cosmic rays are the decay products of cosmological remnants or topological defects associated, for instance, with Grand Unified theories with unification energy M GUT ∼ 10 24 eV. These models predict neutrino fluxes most likely within reach of first-generation telescopes such as AMANDA, and certainly detectable by future kilometer-scale neutrino observatories [10]. They have not been observed.…”