  We investigate gravitational UV/IR mixing models that predict a breakdown of
low energy effective field theory, from loop-level, non-local gravitational
corrections to particle processes. We determine how the choice of IR cutoff in
these theories alters predictions for lepton magnetic moments. Using Brookhaven
E821 muon magnetic moment data, we exclude models of UV/IR mixing with an IR
cutoff set by a spherical volume enclosing the experiment. On the other hand,
an IR cutoff defined by the simply-connected spatial volume containing the
trajectories of the muons, implies a correction to the muon magnetic moment
which may have already been observed.
