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 $k_{\rm eq} \propto \Omega_0 h^2$.