Cosmic microwave background radiation

Neutrino masses as small as 0.1 eV may lead to observable effects in the CMB anisotropies. Pastor reviewed [52] the cosmological implications of large lepton asymmetries, e.g., generated by an Affleck-Dine [53] scenario or active-sterile mixing. In addition to the BBN effects, the asymmetry increases the radiation density and postpones the onset of matter domination. This would suppress the CMB power spectrum on small scales even for $m_\nu =0$, with larger effects for $m_\nu \ne 0$. Masses as small as $10^{-2}$ eV might be observable in the presence of an asymmetry.

Mangano [54] reviewed precision cosmology, emphasizing the interplay between BBN, CMB, and large scale structure data. He described the implications of the recent MAXIMA and BOOMERANG CMB data, which indicate a suppressed second Doppler peak. Several models of the cosmological parameters fit the new data, but should be separable in future (MAP, PLANCK) data on the third peak. One possibility is to increase the baryon density $h^2 \Omega_B$ to a higher value ( $0.030^{+0.012}_{-0.006}$) than is allowed by the BBN data in (). One rather creative resolution would be to somehow increase to $4 < n_{\rm active}^{\rm eff} + n_{\rm sterile}^{\rm eff} < 13$, with 8 favored, and to simultaneously assume a large $\Delta L_e \sim 0.24 \mu_{\nu_e}/T$, corresponding to $0.07 < \mu_{\nu_e}/T < 0.43$, where $\mu_{\nu_e}$ is the $\nu_e$ chemical potential.