If the three active neutrinos mix with a sterile one, i.e., in 3+1 scenarios, they may modify the flavor composition of high-energy astrophysical neutrinos. We analytically derived boundaries in flavor space to avoid having to sample over unknown mixing and help boost searches for new physics (we provided them in nice downloadable data tables, too):
Flavors of Astrophysical Neutrinos with Active-Sterile Mixing Markus Ahlers, Mauricio Bustamante, Niels Gustav Nortvig Willesen https://arxiv.org/abs/2009.01253
The solid lines are the new 3+1 boundaries, computed for the three benchmark production scenarios (three different colors), compared to the boundaries that we computed for three-flavor mixing (dashed lines) in our earlier paper (1810.00893):
Where are the IceCube high-energy astrophysical neutrinos coming from? We don’t know yet! But if the neutrino sources harbor large magnetic fields, then maybe they will leave imprints (due to synchrotron radiation) on the neutrino flux. We looked for these imprints in public IceCube data:
The deadline for submission of letters of interest (LoIs) for the US Snowmass 2021 process was Monday, August 31. There were ~1600 LoIs submitted and all of them can be found here: https://snowmass21.org/loi .
I was personally involved in or led a few:
Cosmic Neutrino Probes of Fundamental Physics [pdf]
To place my new limts, I put to practice a proposal that we published earlier (1610.02096), that uses the observation of the Glashow resonance in IceCube, at a few PeV, as evidence of the survival of nu_1 and nu_2.
I base our present-day results on the observation of the first Glashow resonance candidate by IceCube. For nu_2, the limit on the lifetime is the best one to date. For nu_1, it is comparable to the best one to date, coming from solar neutrinos. The limits quickly improve with just a handful more of Glashow resonances observed.
Recently I was interviewed by El Comercio, the largest national newspaper in Perú, about neutrinos, particles physics, and my Villum Young Investigator grant. The interview appeared online and in print form on February 22, 2020. Here is a link to the online version (in Spanish):
Using high-energy astrophysical neutrinos, with TeV-PeV energies, we have placed limits on secret neutrino-neutrino interactions for mediator masses in the 1-100 MeV range.
While propagating to Earth, high-energy astrophysical neutrinos may interact resonantly with the cosmic neutrino background. This would introduce a gap in the energy spectrum of the high-energy neutrinos. We looked for this gap in 6 years of publicly available IceCube High Energy Starting Events (HESE).
This complements our earlier work (1912.09115), which used supernova neutrinos to place limits on secret interactions, both from neutrino interactions inside the supernova core and from the propagation of neutrinos to Earth (these are the regions labeled “Shashank et al.” in the plot above).
We find limits on the mass and coupling of the new mediator through which the secret interactions occur. For mediator masses between 10 MeV and 15 GeV, our limits are the strongest to date. For mediator masses above 100 MeV, our limits are the first.