The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole Ipeak = (197 +/- 6), with an amplitude delta T200 = (69 +/- 8) microK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.

This paper presents a measurement of the angular power spectrum of the Cosmic Microwave Background from ℓ = 75 to ℓ = 1025 (∼ 10 ′ to 2.4 o ) from a combined analysis of four 150 GHz channels in the BOOMERANG experiment. The spectrum contains multiple peaks and minima, as predicted by standard adiabatic-inflationary models in which the primordial plasma undergoes acoustic oscillations. These results, in concert with other types of cosmological measurements and theoretical models, significantly constrain the values of Ω tot , Ω b h 2 , Ω c h 2 and n s .

Recent results from BOOMERANG-98 and MAXIMA-1, taken together with COBE DMR, provide consistent and high signal-to-noise measurements of the cosmic microwave background power spectrum at spherical harmonic multipole bands over 2

Three peaks and two dips have been detected in the power spectrum of the cosmic microwave background from the BOOMERANG experiment, at ℓ ∼ 210, 540, 840 and ℓ ∼ 420, 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 7-dimensional parameter space of such models, which gives good agreement with the model-independent estimates, and 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 7-dimensional cosmological parameter space, using an independent computational pipeline, and find excellent agreement: Ω tot = 1.02 +0.06 −0.05 vs. 1.04±0.05, Ω b h 2 = 0.022 +0.004 −0.003 vs. 0.019 +0.005 −0.004 , and n s = 0.96 +0.10 −0.09 vs. 0.90±0.08. The deviation in primordial spectral index n s is a consequence of the strong correlation with the optical depth.

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...