Correlated Adiabatic and Isocurvature Cosmic Microwave Background Fluctuations in the Wake of the Results from the Wilkinson Microwave Anisotropy Probe

In general correlated models, in addition to the usual adiabatic component with a spectral index nad1 there is another adiabatic component with a spectral index nad2 generated by entropy perturbation during inflation. We extend the analysis of a correlated mixture of adiabatic and isocurvature cosmic microwave background fluctuations of the Wilkinson Microwave Anisotropy Probe (WMAP) group, who set the two adiabatic spectral indices equal. Allowing nad1 and nad2 to vary independently we find that the WMAP data favor models where the two adiabatic components have opposite spectral tilts. Using the WMAP data only, the 2σ upper bound for the isocurvature fraction fᵢₛₒ of the initial power spectrum at k₀=0.05 Mpc^-1 increases somewhat, e.g., from 0.76 of nad2=nad1 models to 0.84 with a prior nᵢₛₒ<1.84 for the isocurvature spectral index.