Here is a link to the video of my survey talk in the 1st EuCAPT Symposium (slides here): High-energy and ultra-high-energy cosmic neutrinos

Scientific American wrote an article about the multiple ongoing projects planning to detect ultra-high-energy neutrinos via radio: Searching for the Universe’s Most Energetic Particles, Astronomers Turn on the Radio

(Yours truly makes an appearance.)

Thanks to Katrina Miller for the article!

Recently I gave an online introductory talk about neutrinos in the Thursday Morning Science seminar series of the University of L’Aquila. Here is the recording of that (sorry about the audio problems at the beginning!):

The Niels Bohr International Academy (NBIA) invites PhD students and advanced Master students to the International PhD Summer School on Neutrinos: Here, There & Everywhere. This one-week school aims to bring the participants up to date with the latest developments in neutrino physics, from theoretical issues to experimental results, including astrophysical and cosmological aspects.

Students will be given topical introductions, along with an overview of the current state of the field and the open questions that confront it. The invited lecturers are internationally renowned experts in their fields. The school participants will gain a broad understanding of current theoretical problems in neutrino physics, state-of-the-art neutrino experiments, and applications of neutrinos in cosmology and astrophysics.

School dates: July 5-9, 2021

Registration and information: https://www.nbia.dk/neutrino2021

Registration deadline: March 31, 2021 (please register early)

Format: We are presently planning an in-person meeting, but we want to keep everyone safe, so we may revisit the school format if it becomes necessary or advisable due to travel or health restrictions

Participation fee: None

Questions: Please contact the organizers, Markus Ahlers (markus.ahlers@nbi.ku.dk) and Mauricio Bustamante (mbustamante@nbi.ku.dk)

There is a vast potential in using the measurement of the flavor composition of high-energy (TeV-PeV) astrophysical neutrinos to test astrophysics and fundamental physics. But there is also plenty of uncertainty in the prediction of the allowed flavor composition at Earth, due to the uncertainties in the mixing parameters, and in the measurement of flavor composition in neutrino telescopes. In other words, flavor is a powerful tool, but it needs sharpening.

In our latest paper, we show that in the next 20 years, flavor will become the sharp tool it was always meant to be, thanks to new oscillation experiments and new neutrino telescopes:

The Future of High-Energy Astrophysical Neutrino Flavor Measurements
Ningqiang Song, Shirley Weishi Li, Carlos A. Argüelles, Mauricio Bustamante, Aaron C. Vincent
https://arxiv.org/abs/2012.12893

By 2040, we will be able to use flavor composition by itself to identify the production mechanism of high-energy astrophysical neutrinos:

The big POEMMA paper is finally out! It contains the science case, goals, and design of POEMMA, a twin-satellite experiment to detect the fluorescence and Cherenkov emission from extensive air showers triggered by ultra-high-energy cosmic rays and neutrinos in the atmosphere.

The POEMMA (Probe of Extreme Multi-Messenger Astrophysics) Observatory
A.V. Olinto et al.
https://arxiv.org/abs/2012.07945

My own small contribution was mainly on the opportunities for beyond-the-Standard-Model neutrino opportunities at ultra-high energies.

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:

Using High-Energy Neutrinos As Cosmic Magnetometers
Mauricio Bustamante & Irene Tamborra
https://arxiv.org/abs/2009.01306

We exclude large magnetic fields of 10 kG–10 MG:

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]
• Neutrino cross-sections and interaction physics [pdf] (with Amy Connolly & Spencer Klein)
• New physics with astrophysical neutrino flavor [pdf] (with Carlos Argüelles, Teppei Katori, Ali Kheirandish, Sergio Palomares-Ruiz, Jordi Salvadó, Aaron Vincent)
• Ultra-High-Energy Neutrinos [pdf] (with Peter Denton & Stephanie Wissel)
• Target of Opportunity Observations with Next-Generation High-energy Neutrino Observatories [pdf] (with Claire Guépin & Tonia Venters)
• An Andean Deep-Valley Detector for High-Energy Tau Neutrinos [pdf] (with Carlos Argüelles & Andrés Romero-Wolf)
• GRAND: Giant Radio Array for Neutrino Detection [pdf]

Here is a plot I prepared, with feedback from many others, for Cosmic Probes of Fundamental Physics:

In a new paper, I place new limits on the lifetime of the nu_1 and nu_2 neutrinos, assuming they decay into a visible nu_3, in the inverted neutrino mass ordering:

New limits on neutrino decay from the Glashow resonance of high-energy cosmic neutrinos
Mauricio Bustamante
arXiv: 2004.06844

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.