  The flavor composition of high-energy astrophysical neutrinos can reveal the
physics governing their production, propagation, and interaction. The IceCube
Collaboration has published the first experimental determination of the ratio
of the flux in each flavor to the total. We present, as a theoretical
counterpart, new results for the allowed ranges of flavor ratios at Earth for
arbitrary flavor ratios in the sources. Our results will allow IceCube to more
quickly identify when their data imply standard physics, a general class of new
physics with arbitrary (incoherent) combinations of mass eigenstates, or new
physics that goes beyond that, e.g., with terms that dominate the Hamiltonian
at high energy.
