Figures 4-6

*Figure 4*

Baryon drag and its potential dependence. Baryon inertia
in the fluid displaces the zero point of the temperature oscillations
leading to alternating peak heights as a function of scale at last
scattering. The magnitude of the displacement is $R_*\Psi(\eta_*)$, and by
removing it the monotonic variation of heights due to the
potential envelope is uncovered (upper panel). The fractional
effect is of order $R_*\Psi(\eta_*,k)/\Psi(0,k)$ and
can be adequately described by the matter transfer function $T(k)$
(lower panel).
The model here is
CDM with $\Omega_0=1$, $h=1$ and $\Omega_bh^2 = 0.025$.

*Figure 5*

Uncovering Baryon Drag in a low baryon universe.
Diffusion damping obscures the baryon drag signal especially in a
low baryon universe (here $\Omega_b h^2=0.075$ in an otherwise
standard CDM model). Employing the numerical calibration of the
damping tail, we recover the alternations.

*Figure 6*

Potential Envelope. Decay of the potential due to the self
gravity of the photon-baryon fluid drives the oscillator. Comparing
two CDM models with differing matter to radiation ratios $\Omega_0 h^2$,
we see that the oscillations are multiplied by an envelope that
depends on the equality scale $k_{\rm eq} \propto \Omega_0 h^2$.