Figures 7-9
Figure 7
Photon diffusion scale. The photon diffusion scale grows rapidly
near last scattering due to the increasing mean free path of the
photons but remains well under the horizon scale
$k_*^{-1} = (\dot a/a)|_{a_*}$ at last scattering. The small
difference between $a_*$ and $a_d$ is sufficient to cause a
significant difference in the effective damping if $\Omega_b h^2$ differs
substantially from the crossover point $0.03$. The inclusion of
the angular dependence of Compton scattering enhances damping by
a small factor $f_2 = 9/10$ as does the further inclusion of polarization
$f_2 = 3/4$.
Figure 8
Baryon drag effect in adiabatic CDM models.
(a) Baryons cause a drag effect on the photons
leading to a temperature enhancement of $-R\Psi = |R\Psi|$ inside
potential wells which shifts the zero point of the oscillation
(short dashed lines).
(b) This contribution yields alternating peak heights in the rms
and is also retained after
diffusion damping. Here numerical results are displayed.
Figure 9
The residual baryon drag effect after
last scattering in an adiabatic CDM model.
On scales under the width of the visibility
function, cancellation between contributions
which came from potential wells and hills at last scattering
damps fluctuations from the baryon drag effect. Note that
cancellation damping is weak and scales as
$(k\eta_*)^{-1/2}$ in contrast to the exponential diffusion
damping. Projection relates the rms fluctuation in (a) to the
anisotropy power spectrum in (b).