196,037 research outputs found
Standardizing the gamma-ray bursts with the Amati Ep,i-Eiso relation: the updated Hubble diagram and implications for cosmography
No full textHow to measure the curvature of space-time
No full textWe propose a new method of measuring the curvature of space-time using test particles. We show that to determine the curvature of space-time in vacuum it is necessary to use at least four test particles and in general at least six
Two viable quintessence models of the Universe: Confrontation of theoretical predictions with observational data
No full textWe use some of the recently released observational data
to test the viability of two classes of minimally coupled scalar
field models of quintessence with exponential potentials for which
exact solutions of the Einstein equations are known. These models
are very sturdy, depending on only one parameter – the Hubble
constant. To compare predictions of our models with observations
we concentrate on the following data: the power spectrum of the
CMBR anisotropy as measured by WMAP, the publicly available data
on type Ia supernovae, and the parameters of large scale structure
determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS).
We use the WMAP data on the age of the universe and the Hubble
constant to fix the free parameters in our models. We then show
that the predictions of our models are consistent with the
observed positions and relative heights of the first 3 peaks in
the CMB power spectrum, with the energy density of dark energy as
deduced from observations of distant type Ia supernovae, and with parameters of the large scale structure as determined by
2dFGRS, in particular with the average density of dark matter. Our
models are also consistent with the results of the Sloan Digital
Sky Survey (SDSS). Moreover, we investigate the evolution of
matter density perturbations in our quintessential models, solve
exactly the evolution equation for the density perturbations, and
obtain an analytical expression for the growth index f. We
verify that the approximate relation also holds in our models
PECULIAR VELOCITIES FIELD AND THE MATTER DENSITY OF THE UNIVERSE IN SCALAR FIELD QUINTESSENCE MODELS
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Approximate angular diameter distance in a locally inhomogeneous universe with nonzero cosmological constant
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