Cosmological parameters from the first results of Boomerang

Abstract

The anisotropy of the cosmic microwave background radiation contains information about the contents and history of the universe. We report new limits on cosmological parameters derived from the angular power spectrum measured in the first Antarctic flight of the Boomerang experiment. Within the framework of inflation-motivated adiabatic cold dark matter models, and using only weakly restrictive prior probabilites on the age of the universe and the Hubble expansion parameter h, we find that the curvature is consistent with flat and that the primordial fluctuation spectrum is consistent with scale invariant, in agreement with the basic inflation paradigm. We find that the data prefer a baryon density Ω b h 2 above, though similar to, the estimates from light element abundances and big bang nucleosynthesis. When combined with large scale structure observations, the Boomerang data provide clear detections of both dark matter and dark energy contributions to the total energy density Ωtot, independent of data from high redshift supernovae.The angular power spectrum C ℓ of temperature anisotropy in the cosmic microwave background (CMB) is a powerful probe of the content and nature of the universe. The DMR instrument on the COBE satellite measured C ℓ for multipoles ℓ ∼ < 20, corresponding to angular scales ∼ > 7• [1]. Significant experimental effort by many groups focusing on smaller angular scales, when combined [2,3,4], led to the C ℓ estimates in the ℓ bands marked with x's in Figure 1, which indicate a peak at ℓ ∼ 200 [5]. It has long been recognized that if C ℓ can be determined with high precision over these angular scales, parameters such as the total energy density and baryon content of the universe, and the shape of the primordial power spectrum of density fluctuations, can be accurately measured [6]. The most recently published Boomerang angular power spectrum shown in Figure 1 represents a qualitative step towards such high precision [7] (hereafter, B98).The data define a strong peak at ℓ ∼ 200. The steep drop in power from ℓ ∼ 200 to ℓ ∼ 400 is consistent with the structure expected from acoustic oscillations in adiabatic cold dark matter (CDM) models of the universe, but is not consistent with the locations and widths of peaks expected in the simplest cosmic string, global topological defect, and isocurvature perturbation models [8]. The data at higher ℓ show strong detections which limit the height of a second peak, but are consistent with the height expected in many CDM models.In this paper, we concentrate on determining a set of 7 cosmological parameters that characterize a very broad class of CDM models by statistically confronting the theoretical C ℓ 's with the B98 and DMR data. Sample CDM models that fit the data are shown in Figure 1. These are best-fit theoretical models using successively more restrictive "prior probabilities" on the parameters. A major theme of this paper is to illustrate explicitly how inferences that are drawn from the CMB data depend on the priors that are assumed. Some of th...

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