  Lorentz-violating operators involving Standard Model fields are tightly
constrained by experimental data. However, bounds are more model-independent
for Lorentz violation appearing in purely gravitational couplings. The
spontaneous breaking of Lorentz invariance by the vacuum expectation value of a
vector field selects a universal rest frame. This affects the propagation of
the graviton, leading to a modification of Newton's law of gravity. We compute
the size of the long-range preferred-frame effect in terms of the coefficients
of the two-derivative operators in the low-energy effective theory that
involves only the graviton and the Goldstone bosons.
