  We investigate the effect of supersonic relative velocities between baryons
and dark matter, recently shown to arise generically at high redshift, on
baryonic acoustic oscillation (BAO) measurements at low redshift. The amplitude
of the relative velocity effect at low redshift is model-dependent, but can be
parameterized by using an unknown bias. We find that if unaccounted, the
relative velocity effect can shift the BAO peak position and bias estimates of
the dark energy equation-of-state due to its non-smooth, out-of-phase
oscillation structure around the BAO scale. Fortunately, the relative velocity
effect can be easily modeled in constraining cosmological parameters without
substantially inflating the error budget. We also demonstrate that the presence
of the relative velocity effect gives rise to a unique signature in the galaxy
bispectrum, which can be utilized to isolate this effect. Future dark energy
surveys can accurately measure the relative velocity effect and subtract it
from the power spectrum analysis to constrain dark energy models with high
precision.
