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

 

We revamped the bi-weekly NBIA Astroparticle Journal Club, including giving it a new webpage: https://sites.google.com/view/nbia-astro-jc/home .

Each week, there will be a different discussion leader, and 3-4 papers will be presented informally during 10-15 minutes.

The webpage contains the list of papers that will potentially be discussed each week.

Following the GRAND white paper, Popular Mechanics also wrote about GRAND, with a catchy title:

Scientists Want to Build a Telescope the Size of Nebraska

Prompted by the appearance of the GRAND white paper on arXiv, Gizmodo talked to Stephanie Wissel from Cal Poly and me and wrote an article about GRAND:

Astronomers Propose Huge New Telescope System to Understand the Most Energetic Particles Ever Detected

 

The white paper of the Giant Radio Array for Neutrino Detection (GRAND) is finally out on arXiv:

The Giant Radio Array for Neutrino Detection (GRAND): Science and Design, 1810.09994
GRAND Collaboration

I was editor and contributor of this paper — I am part of the GRAND Collaboration.  Being editor demanded considerable time investment.  So it is personally very satisfying to see the paper finally out!

At high energies, new physics might affect the flavor composition of astrophysical neutrinos.  In a large class of new-physics models, the total number of neutrinos of all flavors is conserved.  In other words, the connection between the neutrino flavor states and the neutrino propagation states is represented by a unitary mixing matrix, whose elements have unknown or weakly bounded values.  The new physics is expected to affected the flavor composition of high-energy astrophysical neutrinos, possibly significantly.

In a new paper, led by Markus Ahlers, we show that it is not necessary to know the values of the elements of the new mixing matrix in order to map the effect of new physics on the flavor composition.  Based solely on the unitary of the new matrix, we derive the boundaries of regions that enclose all of the possible flavor compositions expected at Earth.

The regions we derive are refined and generalized versions of earlier work [X.-J. Xu, H.-J. He, and W. Rodejohann, JCAP 1412 (2014) 039, arXiv:1407.3736], and presented in a streamlined formalism that is easy to use.  Neutrino telescopes such as IceCube could adopt these regions as priors in their searches for new physics in the flavor composition.

Read the preprint here:

Unitarity Bounds of Astrophysical Neutrinos, 1810.00893
Markus Ahlers, Mauricio Bustamante, Siqiao Mu

Following the appearance of the preprint

The ANITA Anomalous Events as Signatures of a Beyond Standard Model Particle, and Supporting Observations from IceCube, 1809.09615
Derek B. Fox, Steinn Sigurdsson, Sarah Shandera, Peter Mészáros, Kohta Murase, Miguel Mostafá, Stephane Coutu ,

I was interviewed by Live Science about the ANITA anomalous events.  Here is the link to that:

Bizarre Particles Keep Flying Out of Antarctica’s Ice, and They Might Shatter Modern Physics