The origin of ultra-high energy cosmic rays (UHECR) has been widely regarded as one of
the major questions in the frontiers of particle astrophysics. Gamma ray bursts (GRB), the
most violent explosions in the universe second only to the Big Bang, have been a popular
candidate site for UHECR productions. The recent IceCube report on the non-observation of
GRB induced neutrinos therefore attracts wide attention. This dilemma requires a
resolution: either the assumption of GRB as UHECR accelerator is to be abandoned or the
expected GRB induced neutrino yield was wrong. It has been pointed out that IceCube has
overestimated the neutrino flux at GRB site by a factor of ~5. In this paper we point
out that, in addition to the issue of neutrino production at source, the neutrino
oscillation and the possible neutrino decay during their flight from GRB to Earth should
further reduce the detectability of IceCube, which is most sensitive to the muon-neutrino
flavor as far as point-source identification is concerned. Specifically, neutrino
oscillation will reduce the muon-neutrino flavor ratio from 2/3 per neutrino at GRB source
to 1/3 on Earth, while neutrino decay, if exists and under the assumption of normal
hierarchy of mass eigenstates, would result in a further reduction of muon-neutrino ratio
to 1/8. With these in mind, we note that there have been efforts in recent years in
pursuing other type of neutrino telescopes based on Askaryan effect, which can in
principle observe and distinguish all three flavors with comparable sensitivities. Such
new approach may therefore be complementary to IceCube in shedding more lights on this
cosmic accelerator question.