  A search for sidereal modulation in the flux of atmospheric muon neutrinos in
IceCube was performed. Such a signal could be an indication of
Lorentz-violating physics. Neutrino oscillation models, derivable from
extensions to the Standard Model, allow for neutrino oscillations that depend
on the neutrino's direction of propagation. No such direction-dependent
variation was found. A discrete Fourier transform method was used to constrain
the Lorentz and CPT-violating coefficients in one of these models. Due to the
unique high energy reach of IceCube, it was possible to improve constraints on
certain Lorentz-violating oscillations by three orders of magnitude with
respect to limits set by other experiments.
