Searching for MeV-Scale Gauge Bosons with IceCube
  Light gauge bosons can lead to resonant interactions between high-energy
astrophysical neutrinos and the cosmic neutrino background. We study this
possibility in detail, considering the ability of IceCube to probe such
scenarios. We find the most dramatic effects in models with a very light $Z'$
($m_{Z'} \lesssim 10$ MeV), which can induce a significant absorption feature
at $E_{\nu} \sim\,$5-10$\,{\rm TeV} \times (m_{Z'}/{\rm MeV})^2$. In the case
of the inverted hierarchy and a small sum of neutrino masses, such a light $Z'$
can result in a broad and deep spectral feature at $\sim\,$0.1-10$\,{\rm PeV}
\times (m_{Z'}/{\rm MeV})^2$. Current IceCube data already excludes this case
for a $Z'$ lighter than a few MeV and couplings greater than $g\sim10^{-4}$. We
emphasize that the ratio of neutrino flavors observed by IceCube can be used to
further increase their sensitivity to $Z'$ models and to other exotic physics
scenarios.
