Stability of small-scale baryon perturbations during cosmological recombination

Understand

In this paper, we study small-scale fluctuations (baryon pressure sound waves) in the baryon fluid during recombination.

• In particular, we look at their evolution in the presence of relative velocities between baryons and photons on large scales ($k \sim 10^{-1} \ {\rm Mpc}^{-1}$), which are naturally present during the era of decoupling.
• Previous work concluded that the fluctuations grow due to an instability of sound waves in a recombining plasma, but that the growth factor is small for typical cosmological models.
• These analyses model recombination in an inhomogenous universe as a perturbation to the parameters of the homogenous solution.