### [1005.2416] Relative velocity of dark matter and baryonic f

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**May 17 2010**This is a very interesting paper, which looks at the second-order effect of baryon velcoties on the small-scale matter power spectrum and halo formation. The basic idea is that in regions of space where the baryon velocity was large at the end of recombination the fast bulk flow of the baryons relative to the small-scale dark matter perturbations washes away any baryon overdensity and hence suppresses growth of structure. The effect is therefore a bit like local non-Gaussianity, where here the small-scale matter perturbations are modulated by the large-scale baryon velocities. The paper finds a large effect on the bias, which become scale-dependent.

I was confused by Fig 2, but I think this is [tex]\Delta_m^2[/tex] rather than [tex]\Delta_c^2[/tex], so there is a fall-off in the linear result about the Jeans scale though I can't quite reproduce the same shape for the linear result.

I was confused by Fig 2, but I think this is [tex]\Delta_m^2[/tex] rather than [tex]\Delta_c^2[/tex], so there is a fall-off in the linear result about the Jeans scale though I can't quite reproduce the same shape for the linear result.