Microwave anisotropies from cosmic defects

Coulson, David; Ferreira, Pedro G.; Graham, P. J.; Turok, Neil

doi:10.1038/368027a0

Cited by 78 publications

(80 citation statements)

References 12 publications

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“…It has been suggested that the distribution of temperature differences is a better test of non-Gaussianity than the temperature distribution [16,17]. In Fig.…”

Section: Fig 3 Plotted Is the Rms Anisotropy After Smoothing With Amentioning

confidence: 99%

Large Angular Scale Anisotropy in Cosmic Microwave Background Induced by Cosmic Strings

et al. 1996

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We simulate the anisotropy in the cosmic microwave background (CMB) induced by cosmic strings. By numerically evolving a network of cosmic strings we generate full-sky CMB temperature anisotropy maps. Based on 192 maps, we compute the anisotropy power spectrum for multipole moments ᐉ # 20. By comparing with the observed temperature anisotropy, we set the normalization for the cosmic string mass per unit length m, Cosmic strings are topological defects which may have formed in the very early Universe and may be responsible for the formation of large-scale structure observed in the Universe today [1]. In order to test the hypothesis that the inhomogeneities in our Universe were induced by cosmic strings one must compare observations of our Universe with the predictions of the cosmic string model. This Letter presents results of detailed computations of the large angular scale cosmic microwave background (CMB) anisotropies induced by cosmic strings [2]. These predictions are compared to the large-scale anisotropies observed by the Cosmic Background Explorer (COBE) satellite. Because the predicted temperature perturbations are proportional to the dimensionless quantity Gm͞c 2 where G is Newton's constant and c the speed of light, one may constrain the value of m, the mass per unit length of the cosmic strings. We believe that our estimate of m is the most accurate and reliable to date.Our methodology for computing the large angle anisotropy is to simulate the evolution of random realizations of a cosmic string network [3]. From these network simulations we construct the temperature anisotropy pattern seen by various observers within the simulation volume. We have evolved the strings from a redshift z 100 to the present, in a cubical box whose side length is twice the Hubble radius at the end of the simulation. This large box assures us that the anisotropy pattern is unaffected by the finite simulation volume.In order to obtain the large dynamic range required for these simulations we have used a new technique whereby the number of segments used to represent the string network decreases as the simulation proceeds. We have conducted tests of this method by comparing smaller simulations, with and without decreasing the number of segments: the average long string energy density is unaffected; the distribution of coherent velocities (the string velocity averaged over a particular length scale) is preserved down to scales smaller than 1͞100 of the horizon radius; the effective mass per unit length of string (the energy in string averaged over a particular length scale) is preserved down to scales smaller than 1͞100 of the horizon radius. The decrease in the number of segments was regulated so that on the angular scales of interest the simulation provided a good representation of the cosmic string network. Here we are interested in comparing with data from the COBE differential microwave radiometer (DMR) which measures the anisotropy convolved with an approximately 7 ± FWHM beam [4]. Our contact 0031-9007͞96͞77(15)͞3061(5)...

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“…It has been suggested that the distribution of temperature differences is a better test of non-Gaussianity than the temperature distribution [16,17]. In Fig.…”

Section: Fig 3 Plotted Is the Rms Anisotropy After Smoothing With Amentioning

confidence: 99%

Large Angular Scale Anisotropy in Cosmic Microwave Background Induced by Cosmic Strings

et al. 1996

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“…The implication of this result is that non-Gaussian features cannot be relevant for the large-scale gravitational potential, so, either the primordial fluctuations were indeed Gaussian, or primordial non-random phases were only present on scales below 7 • , as it seems the case for anisotropies generated by topological defects (e.g. Coulson et al 1994, and references therein). Therefore, for the models we consider here, we just have to require that the gravitational potential was significantly non-Gaussian already at redshifts of order of a tenth, when we start to evolve our system, and up to scales as large as ∼ 10 2 Mpc (much below the COBE scale), as probed by our simulations.…”

Section: Introductionmentioning

confidence: 98%

Velocity fields in non-Gaussian cold dark matter models

Lucchin¹,

Matarrese²,

Messina³

et al. 1995

Monthly Notices of the Royal Astronomical Society

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We analyse the large-scale velocity field obtained by N-body simulations of cold dark matter (CDM) models with non-Gaussian primordial density fluctuations, considering models with both positive and negative primordial skewness in the density fluctuation distribution. We study the velocity probability distribution and calculate the dependence of the bulk flow, one-point velocity dispersion and Cosmic Mach Number on the filtering size. We find that the sign of the primordial skewness of the density field provides poor discriminatory power on the evolved velocity field. All non-Gaussian models here considered tend to have lower velocity dispersion and bulk flow than the standard Gaussian CDM model, while the Cosmic Mach Number turns out to be a poor statistic in characterizing the models. Next, we compare the large-scale velocity field of a composite sample of optically selected galaxies as described by the Local Group properties, bulk flow, velocity correlation function and Cosmic Mach Number, with the velocity field of mock catalogues extracted from the N-body simulations. The comparison does not clearly permit to single out a best model: the standard Gaussian model is however marginally preferred by the maximum likelihood analysis.

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“…The in#ationary model predicts Gaussian #uctuations for the statistics of the CMB anisotropies, while alternative models based on the presence of topological defects, such as strings, monopoles, and textures, predict non-Gaussian statistics (e.g. [21]). Due to the di!erent nature of their early history causality constrains primordial perturbations from a source such as in#ation and from topological defects to have a di!erent anisotropy power spectra particularly in the region of the`Dopplera peaks [1].…”

Section: Planck Scientixc Objectivesmentioning

confidence: 99%

CMB anisotropy experiments

Smoot

2000

Physics Reports

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Anisotropies in the cosmic microwave background (CMB) encode information about the evolution and development of the universe. Quality observations of CMB anisotropies can provide a very strong test of cosmological models and provide high precision determination of major cosmological parameters. This paper provides a review of the COBE DMR results, the current status of the measurements of the CMB anisotropy power spectrum and then focuses current and future programs including both suborbital observations and the two selected satellite missions: the NASA MidEX mission MAP and the ESA M3 mission Max Planck Surveyor. This review includes both a description of the experimental programs and the expected quality level of results.

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Microwave anisotropies from cosmic defects

Cited by 78 publications

References 12 publications

Large Angular Scale Anisotropy in Cosmic Microwave Background Induced by Cosmic Strings

Large Angular Scale Anisotropy in Cosmic Microwave Background Induced by Cosmic Strings

Velocity fields in non-Gaussian cold dark matter models

CMB anisotropy experiments

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