Now specifically looking at fluctuation
growth as a function of time on a log-log plot. Scale of 8Mpc or 1014 solar masses.
As the text points out, prior
to recombination, isothermal fluctuations will not grow due
to frictional effects, preserving an initial power
spectrum. After recombination
things change and perturbations can grow. Plot considers adiabatic
fluctuations.
This is NOT my area of
expertise and if you’re interested/motivated, I can
help you follow up on your own.
Kolb and Turner is a good place to start.