NPAC (Nuclear/Particle/Astro/Cosmo) Forums
Organized by: Prof. Lu Lu
Events on Thursday, April 15th, 2021
- Ultra-high-energy cosmic rays and neutrinos, expectations for diffuse fluxes and arrival-direction correlations
- Time: 2:30 pm
- Speaker: Arjen van Vliet, DESY Zeuthen, Germany
- Abstract: Astrophysical neutrinos can be produced by cosmic-ray interactions, either inside the sources of cosmic rays (source neutrinos) or during the propagation through extragalactic space (cosmogenic neutrinos). The expected cosmogenic neutrino flux in the EeV range depends strongly on the composition of ultra-high-energy cosmic rays (UHECRs). A larger fraction of protons will especially increase the expected cosmogenic neutrino flux. One scenario in which a significant proton fraction can be expected is if different classes of Active Galactic Nuclei (AGN) are the dominant sources of UHECRs. If that is the case, not only a large cosmogenic neutrino flux is expected, but a large source neutrino flux as well. It might therefore be interesting to look at correlations between neutrino and UHECR arrival directions. However, deflections of UHECRs in magnetic fields decrease the expected directional correlations. Even for the weakest extragalactic magnetic fields (EGMFs) the non-observation of high-energy neutrino multiplets strongly constrains the possibility to find neutrino-UHECR correlations. On the other hand, the Pierre Auger Collaboration has recently found indications for correlations between UHECR arrival directions and local star-forming galaxies or AGN. These results can be used to put limits on the EGMFs between these galaxies and the Milky Way. For a source density of star-forming galaxies relatively strong EGMFs are required to reproduce the level of anisotropy that Auger has observed.
- Host: Lu Lu