Constraining the Baryon-Dark Matter Relative Velocity with the
  Large-Scale 3-Point Correlation Function of the SDSS BOSS DR12 CMASS Galaxies
  We search for a galaxy clustering bias due to a modulation of galaxy number
with the baryon-dark matter relative velocity resulting from recombination-era
physics. We find no detected signal and place the constraint $b_v < 0.01$ on
the relative velocity bias for the CMASS galaxies. This bias is an important
potential systematic of Baryon Acoustic Oscillation (BAO) method measurements
of the cosmic distance scale using the 2-point clustering. Our limit on the
relative velocity bias indicates a systematic shift of no more than $0.3\%$ rms
in the distance scale inferred from the BAO feature in the BOSS 2-point
clustering, well below the $1\%$ statistical error of this measurement. This
constraint is the most stringent currently available and has important
implications for the ability of upcoming large-scale structure surveys such as
DESI to self-protect against the relative velocity as a possible systematic.
