Quantifying the impact of baryon-CDM perturbations on halo clustering
  and baryon fraction
  Baryons and cold dark matter (CDM) did not comove prior to recombination.
This leads to differences in the local baryon and CDM densities, the so-called
baryon-CDM isocurvature perturbations $\delta_{bc}$. These perturbations are
usually neglected in the analysis of Large-Scale Structure data but taking them
into account might become important in the era of high precision cosmology.
Using gravity-only 2-fluid simulations we assess the impact of such
perturbations on the dark matter halos distribution. In particular, we focus on
the baryon fraction in halos as a function of mass and large-scale
$\delta_{bc}$, which also allows us to study details of the nontrivial
numerical setup required for such simulations. We further measure the
cross-power spectrum between the halo field and $\delta_{bc}$ over a wide range
of mass. This cross-correlation is nonzero and negative which shows that halo
formation is impacted by $\delta_{bc}$. We measure the associated bias
parameter $b_{\delta_{bc}}$ and compare it to recent results, finding good
agreement. Finally we quantify the impact of such perturbations on the
halo-halo power spectrum and show that this effect can be degenerate with the
one of massive neutrinos for surveys like DESI.
