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Neutrinos: astrophysical messengers probing new particle physics

Final Activity Report Summary - ASTRONEUTRINOS (Neutrinos: astrophysical messengers probing new particle physics)

The main objective of the research project consisted in using neutrinos from different astrophysical sources as probe for physics beyond the Standard Model (SM) of particle physics.

The first astrophysical scenario considered has been the core-collapse supernovae (SNe). The motivation has been twofold: First, it is expected that a future SN explosion in our galaxy will lead to an enormous number of neutrino events in the currently running and planned neutrino detectors. Second, the extreme conditions found in SNe may strongly enhance the effect non-standard neutrino properties, in contrast to other neutrino sources.

We have studied the phenomenological consequences of non-standard neutrino interactions (NSI), such as flavour changing neutral currents and violation of universality, for the neutrino propagation through the SN envelope. We have found that for a large range of NSI parameters the behaviour of the neutrinos can be substantially affected. In particular, even for very small values of the NSI parameters, one expects a very specific signature, independent of the uncertainties of the SN models, which would allow to clearly confirming the presence of the NSI, and therefore new physics beyond the SM.

The second scenario analysed has been the high energy neutrinos created by scattered ultra high energy cosmic rays (UHECRs) on background photons. The main motivation has been to study the possibility to avoid the upper limits on the neutrino fluxes obtained by the observed UHECR flux, and get large neutrino fluxes at high energies. Those limits are obtained assuming sources transparent to hadronic interactions. Therefore we have analysed the neutrino yield and flavour content of high energy neutrinos produced in astrophysical opaque sources. First, we have found that for these sources the multiple scattering of nucleons strongly modify the neutrino spectra with respect to transparent sources. The main consequence is a strong suppression of the neutrino flux afrom at high energies. Secondly, these sources present a high energy-dependence of the flavour content of the neutrinos. At the Earth this flavour ratio will have been modulated by oscillation due to the presence of non-vanishing neutrino mixing parameters. Therefore the observation of a strong energy dependence of the neutrino flavour ratio will not only be a hint on the kind of source but also allow obtaining complementary information on non-standard neutrino properties.