Multiple Peaks in the Angular Power Spectrum of the Cosmic Microwave Background: Significance and Consequences for Cosmology

Abstract

Three peaks and two dips have been detected in the power spectrum of the cosmic microwave background by the BOOMERANG experiment, at l = (213), (541), (845) and l = (416), (750), respectively. Using model-independent analyses, we find that all five features are statistically significant, and we measure their location and amplitude. These are consistent with the adiabatic inflationary model. We also calculate the mean and variance of the peak and dip locations and amplitudes in a large seven-dimensional parameter space of such models, which gives good agreement with the model-independent estimates. We forecast where the next few peaks and dips should be found if the basic paradigm is correct. We test the robustness of our results by comparing Bayesian marginalization techniques on this space with likelihood maximization techniques applied to a second seven-dimensional cosmological parameter space, using an independent computational pipeline, and find excellent agreement: Ω_tot = 1.02 versus 1.04 ± 0.05, Ω_bh² = 0.022 versus 0.019, and n_s = 0.96 versus 0.90 ± 0.08. The determination of the best fit by the maximization procedure effectively ignores nonzero optical depth of reionization τ_C > 0, and the difference in primordial spectral index n_s between the two methods is thus a consequence of the strong correlation of n_s with the τ_C.