Results 131 to 140 of about 2,969 (164)

Evolution and classification of cosmological perturbations

Physical Review D, 1989
The evolution of perturbations in a Friedmann universe is investigated by using a new method. In a first step fluctuations of the density, the pressure, and the four-velocity are removed by performing a gauge transformation. Subsequently the problem can be solved and that solution is finally transformed into some important gauges. With the help of this
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Cosmology: the Universe in Evolution

1996
There are three principal pieces of evidence which, when taken together, support the notion that the universe as a whole is evolving. These are: (a) the Hubble velocity-distance relationship; (b) the abundance of light elements in the universe; and (c) the three degree cosmic background radiation.
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Evolution of clusters and cosmology

Astronomische Nachrichten, 2017
Recent Sunyaev–Zeldovich (SZ) surveys (ACT, Planck, SPT) have provided new cluster catalogs, very significantly expanding the coverage of the mass–redshift plane, while XMM‐Newton surveys are pushing cluster detection to lower masses, up to z ∼ 1 and beyond.
Arnaud, M.
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The Cosmological Evolution of Quasars

Physica Scripta, 1978
There is compelling evidence that quasars, both optically selected and radio selected ones, exhibit strong cosmological evolution. If the space density is an exponential of cosmic time, then the characteristic time of decline is one-tenth of the age of the Universe. Quasars with flat radio spectrum appear to show less cosmological evolution.
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Evolution of the cosmological constant

Nature, 1999
Supernova observations have indicated that the Universe is expanding faster than the theory of inflation predicts. Some theoretical cosmologists suggest that an exotic form of energy density called quintessence may be responsible. Quintessence began as Einstein's cosmological constant, but if it is not, in fact, constant it may explain why we appeared ...
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Evolution of Cosmological Fluctuations

2008
Abstract We will now apply the formalism developed in the previous chapter to work out the evolution of cosmological fluctuations, from a temperature 10 K when electron positron annihilation is substantially complete and neutrinos have decoupled from matter and radiation, down to the relatively recent time when the matter fluctuations
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Evolution of cosmological perturbations

2018
AbstractEvolutions equations for cosmological perturbations. Single-component and multi-component fluids. Super-horizon and sub-horizon limits. Adiabatic and isocurvature initial conditions. Analytic and numerical solutions. Power spectra and transfer functions for scalar and tensor perturbations. GW damping from neutrino free-streaming.
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Cosmology and the Evolution of the Universe

2009
This volumes in the Greenwood Guides to the Universe series covers the current scientific understanding of the creation and evolution of the universe. Cosmology and the Evolution of the Universe provides readers with an up-to-date survey of the current scientific understanding of how the universe has evolved in the almost 14 billion years since the Big
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Cosmological evolution of galaxies

2018
The results of an extensive optical and infrared investigation of a complete sub-sample of the Leiden-Berkeley Deep Survey of radio sources at 1.4 GHz are presented. Optical coun­terparts have been identified for 69 of the 73 sources in the two Hercules fields, and redshifts obtained for 49 of them. Photometric redshifts are computed from the griK data
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Cosmological evolution of quintessence and phantom with a new type of interaction in dark sector

Nuclear Physics B, 2011

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