By combining data from seven cosmic microwave background experiments (including the latest WMAP results) with large scale structure data, the Hubble parameter measurement from the Hubble Space Telescope and luminosity measurements of Type Ia supernovae we demonstrate the bounds on the dark energy equation of state wQ to be −1.38 < wQ < −0.82 at the 95% confidence level. Although our limit on wQ is improved with respect to previous analyses, cosmological data does not rule out the possibility that the equation of state parameter wQ of the dark energy Q is less than -1. We present a tracking model that ensures wQ ≤ −1 at recent times and discuss the observational consequences.

We present deep Ka‐band (ν≈ 33 GHz) observations of the cosmic microwave background (CMB) made with the extended Very Small Array (VSA). This configuration produces a naturally weighted synthesized FWHM beamwidth of ∼11 arcmin, which covers an ℓ range of 300 to 1500. On these scales, foreground extragalactic sources can be a major source of contamination to the CMB anisotropy. This problem has been alleviated by identifying sources at 15 GHz with the Ryle Telescope and then monitoring these sources at 33 GHz using a single‐baseline interferometer collocated with the VSA. Sources with flux densities ≳20 mJy at 33 GHz are subtracted from the data. In addition, we calculate a statistical correction for the small residual contribution from weaker sources that are below the detection limit of the survey. The CMB power spectrum corrected for Galactic foregrounds and extragalactic point sources is presented. A total ℓ range of 150–1500 is achieved by combining the complete extended array data with earlier VSA data in a compact configuration. Our resolution of Δℓ≈ 60 allows the first three acoustic peaks to be clearly delineated. This is achieved by using mosaiced observations in seven regions covering a total area of 82 deg2. There is good agreement with the Wilkinson Microwave Anisotropy Probe (WMAP) data up to ℓ= 700 where WMAP data run out of resolution. For higher ℓ values out to ℓ= 1500, the agreement in power spectrum amplitudes with other experiments is also very good despite differences in frequency and observing technique.

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2° at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles ℓ= 160 and 1400. Such measurements at high ℓ are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall‐off in power at high ℓ and starts to constrain the position and height of a fourth peak.

We consider the observational constraints on the running-mass inflationary model, and, in particular, on the scale dependence of the spectral index, from the new cosmic microwave background (CMB) anisotropy measurements performed by WMAP and from new clustering data from the SLOAN survey. We find that the data strongly constraints a significant positive scale dependence of n, and we translate the analysis into bounds on the physical parameters of the inflaton potential. Looking deeper into specific types of interaction (gauge and Yukawa) we find that the parameter space is significantly constrained by the new data, but that the running-mass model remains viable.

The recent measurements of the power spectrum of Cosmic Microwave Background anisotropies are in agreement with the simplest inflationary scenario and big bang nucleosynthesis constraints. However, these results rely on the assumption of a class of models based on primordial adiabatic perturbations, cold dark matter and a cosmological constant. In this paper we investigate the need for deviations from the Λ-CDM scenario by first characterizing the peaks in the spectrum using different phenomenological functions in a 15 dimensional parameter space. Using a Monte Carlo Markov chain approach to Bayesian inference and a low curvature model template we then check for the presence of new physics and/or systematics in the CMB data. We find an almost perfect consistency between the phenomenological fits and the standard Λ-CDM models. However, the curvature of the secondary peaks is weakly constrained by the present data. The improved spectral resolution expected from future satellite experiments is clearly warranted for a definitive test of the scenario.