Imprints of Reionization in Galaxy Clustering
  Reionization, the only phase transition in the Universe since recombination,
is a key event in the cosmic history of baryonic matter. We derive, in the
context of the large-scale bias expansion, the imprints of the epoch of
reionization in the large-scale distribution of galaxies, and identify two
contributions of particular importance. First, the Compton scattering of CMB
photons off the free electrons lead to a drag force on the baryon fluid. This
drag induces a relative velocity between baryons and CDM which is of the same
order of magnitude as the primordially-induced relative velocity, and enters in
the evolution of the relative velocity as calculated by Boltzmann codes. This
leads to a unique contribution to galaxy bias involving the matter velocity
squared. The second important effect is a modulation of the galaxy density by
the ionizing radiation field through radiative-transfer effects, which is
captured in the bias expansion by so-called higher-derivative terms. We
constrain both of these imprints using the power spectrum of the BOSS DR12
galaxy sample. While they do not lead to a shift in the baryon acoustic
oscillation scale, including these terms is important for unbiased cosmology
constraints from the shape of the galaxy power spectrum.
