Constraints on cosmological parameters from recent measurements of CMB anisotropy

A key prediction of cosmological theories for the origin and evolution of structure in the Universe is the existence of a `Doppler peak' in the angular power spectrum of cosmic microwave background (CMB) fluctuations. We present new results from a study of recent CMB observations which provide the first strong evidence for the existence of a `Doppler Peak' localised in both angular scale and amplitude. This first estimate of the angular position of the peak is used to place a new direct limit on the curvature of the Universe, corresponding to a density of

\Omega=0.7^{+0.8}_{-0.5}

, consistent with a flat Universe. Very low density `open' Universe models are inconsistent with this limit unless there is a significant contribution from a cosmological constant. For a flat standard Cold Dark Matter dominated Universe we use our results in conjunction with Big Bang nucleosynthesis constraints to determine the value of the Hubble constant as \ho=30-70\kmspmpc for baryon fractions

\Omega_b=0.05

to 0.2. For \ho=50\kmspmpc we find the primordial spectral index of the fluctuations to be

n=1.1 \pm 0.1

, in close agreement with the inflationary prediction of

n \simeq 1.0

Note:

7 pages LaTeX, including 6 PostScript figures. Accepted for publication in MNRAS

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