Particle Physics Seminar

At the time of recombination, baryons and photons decouple and the sound speed in the baryonic fluid drops from relativistic velocity to the thermal velocity of the hydrogen atoms which is smaller than the relative velocity of baryons and dark matter computed via linear perturbation theory. This leads to formation of supersonic coherent flows of the baryons relative to the underlying dark matter potential wells and subsequent advection of small-scale perturbations by large-scale velocity flows. In this presentation I will discuss the effect of relative velocity of dark matter and baryonic fluids and show how it effects the formation of the first bound objects in the early Universe. I will explain why this effect was previously neglected and under which circumstances it should be taken into consideration. Finally, I will discuss recent results from both analytical and simulation efforts in studying the implications of the relative velocity effect.