Flavor boundaries with high-energy active-sterile neutrino mixing


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

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):

Neutrinos as cosmic magnetometers


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

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

Snowmass 2021 letters of interest


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:

New limits on neutrino decay from the Glashow resonance


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.


Call for PhD position on high-energy cosmic neutrino physics


I am currently looking to hire one PhD student to work with me on high-energy cosmic neutrino physics at the Niels Bohr Institute starting in Fall of 2020.

This is a 3-year position, fully funded by the Villum Fonden program “Pushing neutrino physics to the cosmic frontier.”

Find more details on INSPIRE: https://labs.inspirehep.net/jobs/1781913 .

Application deadline: April 15, 2020

Contact me if you have any questions.

Interview in El Comercio newspaper


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):

Peruano recibe US$15 millones para estudiar los vacíos de la física de partículas

Weirdly, the interview made it to the front page of the print version of newspaper:



Villum Fonden Young Investigator Award


I was recently awarded a Villum Fonden Young Investigator Award (in the amount of ~10M DKK ~= 1.3M euro) to carry out the project “Pushing Neutrino Physics to the Cosmic Frontier”.

This starting grant will allow me to form my own research group at the Niels Bohr Institute, and to fund it for the coming five years. Come Fall 2020, I will become Assistant Professor at the NBI.

More information: https://www.nbi.ku.dk/english/namely_names/2020/three-young-scientists-from-nbi-receive-villum-young-investigator-grants/

New limits on secret neutrino interactions using IceCube neutrinos


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).

Bounds on secret neutrino interactions from high-energy astrophysical neutrinos
Mauricio Bustamante, Charlotte Amalie Rosenstroem, Shashank Shalgar, Irene Tamborra


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).

New supernova limits on secret neutrino interactions


Our paper on new limits on new, secret, neutrino-neutrino interactions beyond the Standard Model from core-collapse supernovae is out:

Core-collapse supernovae stymie secret neutrino interactions (1912.09115)
Shashank Shalgar, Irene Tamborra, Mauricio Bustamante


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.