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Topic: Primordial fluctuations

	Primordial fluctuations - Wikipedia, the free encyclopedia
		Primordial fluctuations are density variations in the early universe which are considered the seeds of all structure in the universe.
		Primordial fluctuations are typically quantified by a power spectrum which gives the power of the variations as a function of spatial scale.
		As with scalar fluctuations, tensor fluctuations are expected to follow a power law and are parameterized by the tensor index (the tensor version of the scalar index), and the ratio of the tensor to scalar power.
	en.wikipedia.org /wiki/Primordial_fluctuations (438 words)

	Tuning in to the early universe (August 2002) - Physics World - PhysicsWeb (Site not responding. Last check: 2007-10-09)
		During inflation the primordial quantum fluctuations that existed at the time of the Big Bang were amplified into macroscopic fluctuations in the density of the universe - fluctuations that eventually formed the large-scale structure of galaxies that we observe today.
		The net result is a series of decreasing peaks in the temperature fluctuations at angles that correspond to a half, a third and a quarter of the angle subtended by the horizon.
		Meanwhile the decline in the strength of the peaks observed by the CBI confirms a fundamental prediction of the standard cosmological theory, namely that we are witnessing the trace of acoustic fluctuations imprinted on the cosmic microwave background.
	physicsweb.org /article/world/15/8/3/1 (1654 words)

	QUIET: Science
		Of particular interest is a tighter constraint on the slope of the primordial spectrum, of prime importance in models of inflation.
		Lensing B-modes In principle, the primordial gravity wave signature is cleanly separable from the polarization from density inhomogeneities by decomposition into E and B components.
		Since the spectrum of lensing fluctuations overlaps in l with the primordial gravity wave spectrum, measurements at both angular scales are necessary to unambiguously detect gravity waves.
	quiet.uchicago.edu /science/index.html (1306 words)

	Physics Today Online - July 2000
		The temperature fluctuations of the CMB are imprints of the point-to-point density fluctuations of the cosmos at the "moment of last scattering." Hotter than average points on the CMB signify regions of above-average mass density.
		The inflationary scenario presumes that density fluctuations of the plasma epoch originated in microscopic primordial quantum fluctuations that were suddenly stretched to astronomical size by inflation.
		Or it might be a suggestion that the spectrum of primordial quantum fluctuations, generally presumed to have been "scale-free," was, perhaps, slightly tilted in favor of spatially larger fluctuations.
	www.aip.org /pt/vol-53/iss-7/p17.html (1961 words)

	A Theoretical Perspective
		Inflation predicts the value of the density parameter of the universe, predicts the spectrum of the primordial fluctuations (although inflation fails to predict its amplitude in a simple way) and their gaussian nature.
		The transfer function T(k) is primarily determined by the dynamics of the primordial fluctuations.
		The reason being that the fluctuations detected by COBE are not so far from what was expected anyway, as the theory was able to predict the shape of the power spectrum over nearly four orders of magnitude in length within a factor of two.
	astro.u-strasbg.fr /howfar/blanchard/theo.html (835 words)

	Galaxy formation and evolution
		Though the formation, and to some extent the evolution of galaxies still is one of the most active research areas in astrophysics, some ideas are now widely accepted.
		After the Big Bang the universe had a period when it was remarkably homogeneous, as can be observed in the Cosmic Background Radiation, the fluctuations of which are less than one part in one hundred thousand.
		The most accepted view is that all the structure we observe today was formed as a consequence of the growing of primordial fluctuations by gravitational instability[?].
	www.ebroadcast.com.au /lookup/encyclopedia/ga/Galaxy_formation.html (701 words)

	A626: Clustering of Dark Matter
		The simplest available hypothesis is that the primordial fluctuation spectrum produces bound structures with length and mass scales growing in direct proportion to the cosmological horizon and the mass contained therein.
		solar masses on the primordial spectrum; fluctuations on smaller scales are highly damped in a `hot' dark matter universe and survive in modified form in a `cold' dark matter universe.
		Observations of temperature fluctuations in the microwave background are consistent with a scale-invariant spectrum with an amplitude on the horizon scale of
	www.ifa.hawaii.edu /faculty/barnes/ast626_95/cdm.html (1290 words)

	Physics Today July 2001
		The square of the lth coefficient measures the mean square spatial temperature fluctuation (or variance) at angular separations near 180°/ l.
		A lower-than-expected second acoustic peak implied one of two possibilities, both quite unpalatable to inflation theorists: Either the primordial spectrum of density fluctuations just before inflation was far from being scale invariant; or the abundance of baryons (protons and neutrons) just after inflation was significantly greater than the theory of primordial nucleosynthesis predicts.
		These very faint spatial fluctuations about the CMB's spectacularly uniform flbody temperature of 2.725 K are measured in microkelvins.
	www.physicstoday.org /pt/vol-54/iss-7/p16.html (1673 words)

	How Did Structure Form in the Universe
		The WMAP satellite measures these small fluctuations in the temperature of the cosmic microwave background radiation and in turn probe the early stages of structure formation.
		These temperature fluctuations are minute: one part of the sky might have a temperature of 2.7251 Kelvin (degrees above absolute zero), while another part might have a temperature of 2.7249 Kelvin.
		For example, the inflationary theory predicts that the largest temperature fluctuations should have an angular scale of one degree, while the defect models predict a smaller characteristic scale.
	www.angelfire.com /space2/chaminda/structure.htm (651 words)

	Theoretical considerations
		Unfortunately there is no fundamental theory for the origin of isothermal fluctuations, and the results for adiabatic fluctuations are usually given concomitantly greater weight.
		If we admit the possibility of isothermal fluctuations as the origin of present-day large-scale structure there is then no barrier, from cosmological considerations, to a purely baryonic universe.
		A baryonic universe might also be consistent with adiabatic fluctuations, but in this case we require the proto-clouds to have sufficiently high density that they decouple from the CMB well ahead of recombination.
	www.atnf.csiro.au /pasa/16_3/walker/paper/node5.html (2141 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		During this epoch, the matter fluctuations, which are bound to develop by the gravitational instability into galaxies, clusters of galaxies and the large-scale structures of the Universe, have a very weak amplitude (few parts per million).
		These density fluctuations generate, at the epoch of the decoupling between matter and radiation, fluctuations of temperatures of the CMB that can be observed today as anisotropies.
		There is therefore a rather direct link between the distribution of energy in the fluctuations at various scales and global information (that cannot be reached by other means) such as the primordial anisotropy spectrum and the cosmological parameters describing the state of the Universe at the moment when the anisotropies were frozen.
	crtbt.grenoble.cnrs.fr /visite_icec/cosmology.html (521 words)

	Kinematic Sunyaev-Zeldovich Effect from Clusters
		Since this effect is independent of frequency, the maximum attainable signal-to-noise ratio for a typical cluster is determined primarily by confusion with the primordial CMB fluctuations.
		The final signal-to-noise ratio depends sensitively on the angular resolution of the instrument and on the temperature power spectrum of the primordial CMB anisotropies (and hence on the cosmological parameters), thus the precise accuracy of peculiar velocity measurements for individual clusters depends on parameters which are poorly known at present (see Figure 1.17).
		PLANCK can therefore provide unique statistical information on bulk motions, which can be used to constrain the power spectrum of matter fluctuations on large scales and to elucidate the relationship between irregularities in the galaxy and mass distribution (Dekel 1994).
	www.rssd.esa.int /SA/PLANCK/include/report/redbook/152.htm (532 words)

	Statistical properties of primordial matter density fields
		one may notice that the long-range order of the distribution corresponds to the presence of mass fluctuations which are depressed with respect to the uncorrelated Poisson case.
		For this reason the super-homogeneous nature of primordial density field is a fundamental property independently on the nature of dark matter.
		The ``primordial'' form of the PS is thus not apparent in that which one would expect to measure from objects selected in this way.
	pil.phys.uniroma1.it /~sylos/test/node4.html (1136 words)

	Galaxy formation
		The key point here is that during inflation small quantum fluctuations get amplified up to enormous cosmological lengthscales - this is a manifestation of Heisenberg's uncertainty principle combined with the rapid expansion.
		In the standard cosmological framework, the gravitational amplification of small primordial density perturbations leads to the formation of bound clumps of dark matter by the process of hierarchical clustering.
		Cooling is very efficient on galactic and subgalactic scales and, in the absence of heating sources, gas is expected to quickly lose its pressure support and collapse to the centre of virialized halos where it eventually turns into stars.
	www.damtp.cam.ac.uk /user/gr/cosmos/legacy/Public/galaxy.html (1092 words)

	The role of dark matter
		In this way they are able to produce the primordial matter density fluctuations field with the appropriate amplitude to be compatible with two important observational constraints at early and late times.
		Primordial density fluctuations have imprinted themselves on the patterns of radiation also, and those variations should be detectable in the Cosmic Microwave Background Radiation (CMBR).
		Thus in these models dark matter plays the dominant role of providing density fluctuation seeds which, from the one hand are compatible with observations of the CMBR (see Fig.
	pil.phys.uniroma1.it /~sylos/test/node3.html (521 words)

	Saleem Zaroubi's fields of interest in Cosmology
		Determining the nature of the primordial fluctuation field is one the main goals of the study of Large Scale Structure.
		The first is to assume, as predicted by simple models of Cosmological-Inflation, that the probability distribution function of the primordial fluctuations is Gaussian and to measure its moments in real or Fourier space, especially the power spectrum.
		In particular the imprint of physical and statistical characteristics of the fluctuation field on the last scattering surface provides a very direct and clean test to the Gaussianity of the primordial fluctuations field, an issue of great importance.
	www.astro.rug.nl /~saleem/research.html (2329 words)

	Cosmology 101: Structures in the Universe
		These fluctuations leave an imprint in the cosmic microwave background radiation in the form of temperature fluctuations from point to point across the sky.
		Tiny variations in the density of matter in the early universe leave an imprint in the cosmic microwave background radiation in the form of temperature fluctuations from point to point across the sky.
		WMAP re-measures the fluctuations with both higher angular resolution and sensitivity.
	map.gsfc.nasa.gov /m_uni/uni_101structures.html (821 words)

	James Robinson Seminar Abstract (Site not responding. Last check: 2007-10-09)
		In this talk I will consider constraints on the amplitude of mass fluctuations in the universe (sigma8) derived from two simple observations: the present number density of clusters and the amplitude of their correlation function.
		Allowing for the possibility that the primordial fluctuations are non-gaussian introduces a degeneracy in the value of sigma8 preferred by each of these constraints, but I will show how taking the constraints together breaks this degeneracy, allowing a simultaneous determination of sigma8 and the degree of non-gaussianity for a given background cosmology.
		For some choices of background cosmology (including favoured low matter density models) the hypothesis that the primordial fluctuations are gaussian is in conflict with the data.
	www-ctp.mit.edu /cosmo/y9899/robinson_abs.html (147 words)

	Primordial black hole - Wikipedia, the free encyclopedia
		A primordial fl hole is a hypothetical type of fl hole that is formed not by the gravitational collapse of a star but by the extreme density of matter present during the universe's early expansion.
		One way to detect primordial fl holes is by their Hawking radiation.
		Even if they do not solve these problems, the low number of primordial fl holes (they have never been detected) aids cosmologists by putting constraints on the spectrum of density fluctuations in the early universe.
	en.wikipedia.org /wiki/Primordial_black_hole (675 words)

	Cosmology -- Early Universe (Site not responding. Last check: 2007-10-09)
		Complications arise because the anisotropy is generated through a variety of physical effects and depends not only on the primordial spectra but also on virtually all cosmological parameters.
		They demonstrated that constraints on compactness follow from the cutoff, but more powerful limits are obtained by exploiting the details of the geodesic structure for each individual topology, and showed this by making maps and undertaking full statistical analyses of the DMR data for selected compact hyperbolic models.
		Dick Bond, Dmitry Pogosyan and Igor Sokolov (Toronto) constrained the size of flat 3-torus and 1-torus topologies using the COBE data by assuming Gaussian fluctuations derived from an inflation epoch, calculating the pixel-pixel temperature correlation function using FFT techniques, and confronting the data using a full linear Bayesian statistical analysis.
	www.cita.utoronto.ca /webpages/CITA/annrep96/node26.html (1206 words)

	Separation of the Foregrounds from the Primordial Fluctuations (Site not responding. Last check: 2007-10-09)
		The expected spectrum of these various components and of their fluctuations are shown as a function of frequency and distribution on the sky in Figures 1.2 and 1.3.
		Similarly, the dust emission from infrared cirrus and from normal spiral galaxies, as well as that from starburst galaxies, are strongest in the highest frequency channel.
		For spiral and starburst galaxies they are dominated by the fluctuations of the background due to weak sources undetected in the highest frequency channel.
	aether.lbl.gov /www/projects/cosa/foregrounds.html (555 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		Primordial fluctuations would be amplified exponentially by cosmic inflation.
		Fluctuations on such a large scale have been found and have been confirmed by other experiments.
		They may be masked by a period of intense star formation in the early universe (at z=100) that re-ionized much of the gas, wiping out small-scale fluctuations.
	www.seds.org /nodes/NODEv4n5-2.5.html (438 words)

	Citebase - On de Sitter deflationary cosmology from the spin-torsion primordial fluctuations and COBE data (Site not responding. Last check: 2007-10-09)
		On de Sitter deflationary cosmology from the spin-torsion primordial fluctuations and COBE data
		Fluctuations on de Sitter solution of Einstein-Cartan field equations are obtained in terms of the matter density primordial density fluctuations and spin-torsion density and matter density fluctuations obtained from COBE data.
		Einstein-de Sitter solution is shown to be unstable even in the absence of torsion.The spin-torsion density fluctuation to generate a deflationary phase is computed from the COBE data.
	citebase.eprints.org /cgi-bin/citations?id=oai:arXiv.org:gr-qc/9912072 (148 words)

	Cosmology (Site not responding. Last check: 2007-10-09)
		Observations of distant galaxies and quasars, measurements of the temperature fluctuations of the microwave background radiation and the X-ray flux from distant clusters of galaxies are all placing strong constraints on cosmological theories.
		The research in cosmology at CITA covers most areas of current interest including studies of the early universe and the origin of the primordial density fluctuations, the connection to the cosmic microwave background (CMB) temperature fluctuations and the nonlinear evolution via gravitational collapse into galaxies, clusters of galaxies and the large-scale structure.
		Measurements from future satellites and ground-based experiments can constrain the fundamental cosmological parameters including the Hubble constant, the universal mean density in dark matter and gas, the shape of the power spectrum of primordial fluctuations and the topology of the universe as a whole.
	www.cita.utoronto.ca /webpages/CITA/annrep96/node20.html (693 words)

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