Flavor composition of high-energy cosmic neutrinos: a map of things to come


The flavor composition of high-energy cosmic neutrinos has long been recognized as a rich probe of particle physics and astrophysics.  We are rapidly making progress in measuring the flavor composition with higher precision.

To take stock of the present situation and of things to come, I chose what I think are some of the most interesting flavor-related questions, and laid them out according to when we will answer them and how easy it will be to answer them.  (Of course, there is some subjectivity involved in where the questions are place.)


Fore more information about the status and future prospects of flavor composition, see my recent talk at PAHEN: Flavor in high-energy cosmic neutrinos: Interpretation and new challenges.

A map of new physics with high-energy neutrinos


There is vast potential to test new physics with high-energy cosmic neutrinos, and the community has started doing it.  As a way to help guide our collective efforts, we came up with a classification scheme of new-physics models:


The scheme classifies models according to the stages of the neutrino lifetime at which they may act — at production, during propagation, at detection — and what observables they may affect — energy spectrum, arrival directions, flavor composition, arrival times.

(The list of models above is representative, not exhaustive.)

For more information see:

NuOscProbExact code and paper released



For a while now, I had been working on a lightweight code to compute neutrino oscillation probabilities for arbitrary oscillation scenarios.

NuOscProbExact uses the method developed by Ohlsson and Snellman to compute probabilities exactly without the need of diagonalizing the Hamiltonian.

NuOscProbExact is fully written in Python 3.7, open source, and publicly available at this GitHub repository: github.com/mbustama/NuOscProbExact .

In the repository you will also find documentation and examples; the code itself is distributed with example files ready to run.



For details, see the accompanying paper:

NuOscProbExact: a general-purpose code to compute exact two-flavor and three-flavor neutrino oscillation probabilities, Mauricio Bustamante, [arXiv:1904.12391]

Article about the PUCP Physics colloquia



For more than 8 years now, I have been organizing the weekly Physics colloquia at my old alma mater, PUCP, in Lima.  By the end of the current semester, we will have had just shy of 280 colloquia.

The university news portal, PuntoEdu, recently wrote a nice bit about the colloquia, with the cool illustration above.  They also mentioned the team of people that recently visited Perú and PUCP to assess the possibility of building the potential future Southern Gamma-ray Suvey Observatory (SGSO) in the Andes of Perú.

Here is the article (in Spanish): Hablemos de física

(Image above copyright of PuntoEdu)

Review on ultra-high-energy cosmic rays


Our review on open questions in ultra-high-energy cosmic rays is now out:

Open Questions in Cosmic-Ray Research at Ultrahigh Energies, 1903.06714


We wrote this review following the 2018 workshop at MIAPP: “The High Energy Universe: Gamma Ray, Neutrino, and Cosmic Ray Astronomy”.  The review will be published in Frontiers.

The figure above is a Hillas plot by Foteini Oikonomou, Fig. 10 in the paper.

Astro2020 neutrino white papers


The US decadal survey in Astronomy and Astrophysics (more information here) requested science white paper for their panel to review.  The recommendations of the panel will help guide decision-making in the next ten years.

A group of us(*) consisting of experimentalists and theorists from across the field have submitted two white papers on high-energy cosmic neutrinos to the survey.  The papers are each endorsed by  >300 members of the community.

Take a look for yourself:

Fundamental Physics with High-Energy Cosmic Neutrinos, 1903.04333


Astrophysics Uniquely Enabled by Observations of High-Energy Neutrinos, 1903.04334


(*) Markus Ackermann, Markus Ahlers, Luis Anchordoqui, Mauricio Bustamante, Amy Connolly, Cosmin Deaconu, Darren Grant, Peter Gorham, Francis Halzen, Albrecht Karle, Kumiko Kotera, Marek Kowalski, Miguel A. Mostafa, Kohta Murase, Anna Nelles, Angela Olinto, Andres Romero-Wolf, Abigail Vieregg, Stephanie Wissel

Long-range neutrino interaction paper picked as PRL Editors’ Suggestion


Our paper ‘Universe’s Worth of Electrons to Probe Long-Range Interactions of High-Energy Astrophysical Neutrinos’ was published on Physical Review Letters:


It was selected as a PRL Editors’ Suggestion.  You can read the synopsis on the APS Physics page here:

Synopsis: Neutrino Probes of Long-Range Interactions

Link to the arXiv version of the paper: 1802.02042

Recovering the neutrino flavor composition at neutrino sources


In a new paper with Markus Ahlers, we introduce a method to infer the flavor composition of high-energy astrophysical neutrinos at their sources, based on measurements of the flavor composition at Earth:

Inferring the flavor of high-energy astrophysical neutrinos at their sources
Mauricio Bustamante, Markus Ahlers

To do this, we effectively revert the effect of flavor oscillations, while taking into account uncertainties in the neutrino mixing parameters.

We apply the method to flavor measurements published by IceCube, and to projections for the near-future IceCube upgrade and the more distant IceCube-Gen2.

In the illustrative, physically motivated case where there is no production of tau neutrinos at the sources, we can recover the fraction of electron neutrinos produced at the sources:


Presently (“IceCube 2015”), we find that neutrino production by the decay of high-energy pions is compatible with the flavor and oscillation data, with a slight preference for sources harboring strong magnetic fields which make intermediate muons lose energy by synchrotron radiation.  In the future, the IceCube ugprade and IceCube-Gen2 have the potential to single out the neutrino production mechanism