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