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Precision Cosmology (precision + cosmology)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Precision cosmology with voids: definition, methods, dynamics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010
Guilhem Lavaux
ABSTRACT We propose a new definition of cosmic voids based on methods of Lagrangian orbit reconstruction as well as an algorithm to find them in actual data called DynamIcal Void Analysis. Our technique is intended to yield results which can be modelled sufficiently accurately to create a new probe of precision cosmology. We then develop an analytical model of the ellipticity of voids found by our method based on the Zel'dovich approximation. We measure in N -body simulation that this model is precise at the ,0.1 per cent level for the mean ellipticity of voids of size greater than ,4 h,1 Mpc. We estimate that at this scale we are able to predict the ellipticity with an accuracy of ,,, 0.02. Finally, we compare the distribution of void shapes in N -body simulation for two different equations of state w of the dark energy. We conclude that our method is far more accurate than Eulerian methods and is therefore promising as a precision probe of dark energy phenomenology. [source]

Transients from initial conditions in cosmological simulations

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006
Martín Crocce
ABSTRACT We study the impact of setting initial conditions in numerical simulations using the standard procedure based on the Zel'dovich approximation (ZA). As it is well known from the perturbation theory, ZA initial conditions have incorrect second- and higher-order growth and therefore excite long-lived transients in the evolution of the statistical properties of density and velocity fields. We also study the improvement brought by using more accurate initial conditions based on second-order Lagrangian perturbation theory (2LPT). We show that 2LPT initial conditions reduce transients significantly and thus are much more appropriate for numerical simulations devoted to precision cosmology. Using controlled numerical experiments with ZA and 2LPT initial conditions, we show that simulations started at redshift zi= 49 using the ZA underestimate the power spectrum in the non-linear regime by about 2, 4 and 8 per cent at z= 0, 1, and 3, respectively, whereas the mass function of dark matter haloes is underestimated by 5 per cent at m= 1015 M, h,1 (z= 0) and 10 per cent at m= 2 × 1014 M, h,1 (z= 1). The clustering of haloes is also affected to the few per cent level at z= 0. These systematics effects are typically larger than statistical uncertainties in recent mass function and power spectrum fitting formulae extracted from numerical simulations. At large scales, the measured transients in higher-order correlations can be understood from first principle calculations based on perturbation theory. [source]

Setting new constraints on the age of the Universe

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001
Ignacio Ferreras
There are three independent techniques for determining the age of the Universe: via cosmochronology of long-lived radioactive nuclei, via stellar modelling and population synthesis of the oldest stellar populations, and, most recently, via the precision cosmology that has become feasible with the mapping of the acoustic peaks in the cosmic microwave background. We demonstrate that all three methods give completely consistent results, and enable us to set rigorous bounds on the maximum and minimum ages that are allowed for the Universe. We present new constraints on the age of the Universe by performing a multiband colour analysis of bright cluster ellipticals over a large redshift range , which allows us to infer the ages of their stellar populations over a wide range of possible formation redshifts and metallicities. Applying a prior to Hubble's constant of we find the age of the Universe to be (1,), in agreement with the estimates from Type Ia supernovae, as well as with the latest uranium decay estimates, which yield an age for the Milky Way of . If we combine the results from cluster ellipticals with the analysis of the angular power spectrum of the cosmic microwave background and with the observations of Type Ia supernovae at high redshift, we find a similar age: . Without the assumption of any priors, universes older than 18 Gyr are ruled out by the data at the 90 per cent confidence level. [source]

What kind of science is cosmology?

ANNALEN DER PHYSIK, Issue 6 2010
H.F.M. Goenner
Abstract In recent years, by theory and observation cosmology has advanced substantially. Parameters of the concordance or ,CDM cosmological model are given with unprecedented precision ("precision cosmology"). On the other hand, 95% of the matter content of the universe are of an unknown nature. This awkward situation motivates the present attempt to find cosmology's place among the (exact) natural sciences. Due to its epistemic and methodical particularities, e.g., as a mathematized historical science, cosmology occupies a very special place. After going through some of the highlights of cosmological modeling, the conclusion is reached that knowledge provided by cosmological modeling cannot be as explicative and secure as knowledge gained by laboratory physics. [source]