THE EARLY UNIVERSE. “Baryon number density is then radiated away from those hot pockets, by diffusion through the relativistic plasma at the speed of sound, s= /3‾√3, until they are homogeneously distributed within a fraction of a second, well before primordial nucleosynthesis.”””
https://royalsocietypublishing.org/doi/10.1098/rsta.2019.0091