  We discuss the importance of flavor ratio measurements in neutrino
telescopes, such as by measuring the ratio between muon tracks to cascades, for
the purpose of extracting new physics signals encountered by astrophysical
neutrinos during propagation from the source to the detector. The detected
flavor ratios not only carry the energy information of specific new physics
scenarios which alter the transition probabilities in distinctive ways, but
also the energy dependent flavor composition at the source. In the present
work, we discuss the interplay of these two energy dependent effects and
identify which new physics scenarios can be distinguished from the detected
flavor ratios as a function of astrophysical parameters. We use a recently
developed self-consistent neutrino production model as our toy model to
generate energy dependent source flavor ratios and discuss (invisible) neutrino
decay and quantum decoherence as specific new physics examples. Furthermore, we
identify potentially interesting classes of sources on the Hillas plot for the
purpose of new physics searches. We find that sources with substantial magnetic
fields 10^3 Gauss <= B <= 10^6 Gauss, such as Active Galactic Nuclei (AGN)
cores, white dwarfs, or maybe gamma-ray bursts, have, in principle, the best
discrimination power for the considered new physics scenarios, whereas AGN
jets, which typically perform as pion beam sources, can only discriminate few
sub cases in the new physics effects. The optimal parameter region somewhat
depends on the class of new physics effect considered.
