arXiv subjects

J. L. Sievers

Publications and source records attributed to J. L. Sievers.

41 records · Page 3Linked to original sources

arXiv2003

Cosmological Parameters from Cosmic Background Imager Observations and Comparisons with BOOMERANG, DASI, and MAXIMA

We report on the cosmological parameters derived from observations with the Cosmic Background Imager (CBI), covering 40 square degrees and the multipole range 300 < l < 3500. The angular scales probed by the CBI correspond to structures which cover the mass range from 10^14 to 10^17 M_sun, and the observations reveal, for the first time, the seeds that gave rise to clusters of galaxies. These unique, high-resolution observations also show damping in the power spectrum to l ~ 2000, which we interpret as due to the finite width of the photon-baryon decoupling region and the viscosity operating at decoupling. Because the observations extend to much higher l the CBI results provide information complementary to that probed by the Boomerang, DASI, Maxima, and VSA experiments. As the observations are pushed to higher multipoles no anomalies relative to standard models appear, and extremely good consistency is found between the cosmological parameters derived for the CBI observations over the range 610 < l < 2000 and observations at lower l [abridged].

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arXiv2002

CMB observations with the Cosmic Background Imager (CBI) Interferometer

We review the recently published results from the CBI's first season of observations. Angular power spectra of the CMB were obtained from deep integrations of 3 single fields covering a total of 3 deg^2 and 3 shallower surveys of overlapping (mosaiced) fields covering a total of 40 deg^2. The observations show a damping of the anisotropies at high-l as expected from the standard scenarios of recombination. We present parameter estimates obtained from the data and discuss the significance of an excess at l>2000 observed in the deep fields.

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arXiv2002

The Cosmic Microwave Background & Inflation, Then & Now

Boomerang, Maxima, DASI, CBI and VSA significantly increase the case for accelerated expansion in the early universe (the inflationary paradigm) and at the current epoch (dark energy dominance), especially when combined with data on high redshift supernovae (SN1) and large scale structure (LSS). There are ``7 pillars of Inflation'' that can be shown with the CMB probe, and at least 5, and possibly 6, of these have already been demonstrated in the CMB data: (1) a large scale gravitational potential; (2) acoustic peaks/dips; (3) damping due to shear viscosity; (4) a Gaussian (maximally random) distribution; (5) secondary anisotropies; (6) polarization. A 7th pillar, anisotropies induced by gravity wave quantum noise, could be too small. A minimal inflation parameter set, ω_b,ω_{cdm}, Ω_{tot}, Ω_Q,w_Q,n_s,τ_C, σ_8}, is used to illustrate the power of the current data. We find the CMB+LSS+SN1 data give Ω_{tot} =1.00^{+.07}_{-.03}, consistent with (non-baroque) inflation theory. Restricting to Ω_{tot}=1, we find a nearly scale invariant spectrum, n_s =0.97^{+.08}_{-.05}. The CDM density, Ω_{cdm}{\rm h}^2 =.12^{+.01}_{-.01}, and baryon density, Ω_b {\rm h}^2 = >.022^{+.003}_{-.002}, are in the expected range. (The Big Bang nucleosynthesis estimate is 0.019\pm 0.002.) Substantial dark (unclustered) energy is inferred, Ω_Q \approx 0.68 \pm 0.05, and CMB+LSS Ω_Q values are compatible with the independent SN1 estimates. The dark energy equation of state, crudely parameterized by a quintessence-field pressure-to-density ratio w_Q, is not well determined by CMB+LSS (w_Q < -0.4 at 95% CL), but when combined with SN1 the resulting w_Q < -0.7 limit is quite consistent with the w_Q=-1 cosmological constant case.

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arXiv2002

Cosmological Parameters from CMB measurements with the CBI

We derive cosmological parameters from the CBI measurements of the Cosmic Microwave Background (CMB) angular power spectrum. Our results provide an independent confirmation of the standard $Ω_{\rm tot}=1$ $Λ$CDM model within the adiabatic, inflationary paradigm. Above $\ell=2000$ the observations show evidence of power in excess of that expected in the standard models. We use hydrodynamical simulations to show how Sunyaev-Zeldovich Effect (SZE) may account for the excess power for models with fluctuation amplitude $σ_8\sim 1$ which is in the high end of the range allowed by the primary CMB observations.

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arXiv2002

A Fast Gridded Method for the Estimation of the Power Spectrum of the CMB from Interferometer Data with Application to the Cosmic Background Imager

We describe an algorithm for the extraction of the angular power spectrum of an intensity field, such as the cosmic microwave background (CMB), from interferometer data. This new method, based on the gridding of interferometer visibilities in the aperture plane followed by a maximum likelihood solution for bandpowers, is much faster than direct likelihood analysis of the visibilities, and deals with foreground radio sources, multiple pointings, and differencing. The gridded aperture-plane estimators are also used to construct Wiener-filtered images using the signal and noise covariance matrices used in the likelihood analysis. Results are shown for simulated data. The method has been used to determine the power spectrum of the cosmic microwave background from observations with the Cosmic Background Imager, and the results are given in companion papers.

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