Cosmic Microwave Background Anisotropy at Degree Angular Scales and the Thermal History of the Universe

We study the anisotropy of the cosmic microwave background (CMB) in cold andmixed dark matter (CDM and MDM) models, with non scale-invariant primordialpower spectra (i.e. $n \neq 1$) and a late, sudden reionization of theintergalactic medium at redshift $z_{rh}$. We test these models against recentdetections of CMB anisotropy at large and intermediate angular scales. We findthat current CMB anisotropy measurements cannot discriminate between CDM andMDM models. Our likelihood analysis indicates that models with blue powerspectra ($n \simeq 1.2$) and a reionization at $z_{rh} \sim 20$ are mostconsistent with the anisotropy data considered here. Without reionization ouranalysis gives $1.0 \le n \le 1.26$ (95 % C.L.) for $\Omega_b = 0.05$.Comment: 14 pages, 4 figures. Submitted to Ap