Figures 13-14

Figure 13

Exotic baryon and radiation content. (a) The sound horizon which forms the basis of the peak-spacing test is independent of $\Omega_b h^2$ for values near BBN or lower, whereas the damping tail is insensitive to high $\Omega_b h^2$. In either limit a robust test exists. The ratio of tail to peak-spacing $\ell_D/\ell_A$ can detect an exotic baryon content. (b) Changing the radiation content, e.g.~by altering the number of relativistic neutrinos $N_\nu$, affects the expansion rate and thus the two physical scales weakly. Cases extreme enough to affect the scales significantly can also be distinguished by $\ell_D/\ell_A$.

Figure 14

Exotic ionization history ($\Omega_0h^2=0.25, \Omega_bh^2=0.0125$). We show the damping and peak-separation scales in a model with instantaneous recombination at $z_*$. For a gradual recombination, a lower $\ell_D/\ell_A$ will always result. The diffusion scale at last scattering by definition approaches the sound horizon in the limit that no recombination (NR) occurred. Assuming instantaneous recombination, the ratio $\ell_D/\ell_A$ roughly corresponds to the number of observable peaks and can be used to discriminate against exotic ionization histories.