62 research outputs found
The Imprint of Gravitational Waves on the Cosmic Microwave Background
Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.Comment: 11 pages, Penn Preprint-UPR-
Merger rates of dark matter haloes: a comparison between EPS and N-body results
We calculate merger rates of dark matter haloes using the Extended
Press-Schechter approximation (EPS) for the Spherical Collapse (SC) and the
Ellipsoidal Collapse (EC) models.
Merger rates have been calculated for masses in the range
to and for
redshifts in the range 0 to 3 and they have been compared with merger rates
that have been proposed by other authors as fits to the results of N-body
simulations. The detailed comparison presented here shows that the agreement
between the analytical models and N-body simulations depends crucially on the
mass of the descendant halo. For some range of masses and redshifts either SC
or EC models approximate satisfactory the results of N-body simulations but for
other cases both models are less satisfactory or even bad approximations. We
showed, by studying the parameters of the problem that a disagreement --if it
appears-- does not depend on the values of the parameters but on the kind of
the particular solution used for the distribution of progenitors or on the
nature of EPS methods.
Further studies could help to improve our understanding about the physical
processes during the formation of dark matter haloes.Comment: 29 pages, 9 figure
Combined constraints on modified Chaplygin gas model from cosmological observed data: Markov Chain Monte Carlo approach
We use the Markov Chain Monte Carlo method to investigate a global
constraints on the modified Chaplygin gas (MCG) model as the unification of
dark matter and dark energy from the latest observational data: the Union2
dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the
cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the
cosmic microwave background (CMB) data. In a flat universe, the constraint
results for MCG model are,
()
,
()
,
()
,
()
, and ()
.Comment: 12 pages, 1figur
Corporatism as a process of working class containment and roll-back: The recent experiences of South Africa and South Korea
In this article we argue that recent debates in the corporatist literature about whether corporatism is best understood as a process of structured interest representation or political dialogue miss the point as to corporatism's central task - the shift of material resources and power away from the working class to the capitalist class, in which two processes are evident - containment and roll-back. We discuss these processes in the context of successive waves of corporatism in Western Europe from the 1940s to the 1990s before moving on to an analysis of the contrasting fortunes of corporatism in South Africa and South Korea during democratic transition. We conclude that the ability of corporatism to carry out the processes of containment and roll back in these two cases have been dependent on the existence (or absence) of supportive prior political relationships between organised labour and the state
Inflation, cold dark matter, and the central density problem
A problem with high central densities in dark halos has arisen in the context
of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is
often justified by appealing to the inflation scenario, inflationary models
with mild deviations from scale-invariance are not uncommon and models with
significant running of the spectral index are plausible. Even mild deviations
from scale-invariance can be important because halo collapse times and
densities depend on the relative amount of small-scale power. We choose several
popular models of inflation and work out the ramifications for galaxy central
densities. For each model, we calculate its COBE-normalized power spectrum and
deduce the implied halo densities using a semi-analytic method calibrated
against N-body simulations. We compare our predictions to a sample of dark
matter-dominated galaxies using a non-parametric measure of the density. While
standard n=1, LCDM halos are overdense by a factor of 6, several of our example
inflation+CDM models predict halo densities well within the range preferred by
observations. We also show how the presence of massive (0.5 eV) neutrinos may
help to alleviate the central density problem even with n=1. We conclude that
galaxy central densities may not be as problematic for the CDM paradigm as is
sometimes assumed: rather than telling us something about the nature of the
dark matter, galaxy rotation curves may be telling us something about inflation
and/or neutrinos. An important test of this idea will be an eventual consensus
on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our
successful models have values of sigma_8 approximately 0.75, which is within
the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1)
are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's
Comments, error in Eq. (18) corrected, references updated and corrected,
conclusions unchanged. Version accepted for publication in Phys. Rev. D,
scheduled for 15 August 200
On the spin distributions of CDM haloes
We used merger trees realizations, predicted by the extended Press-Schechter
theory, in order to study the growth of angular momentum of dark matter haloes.
Our results showed that: 1) The spin parameter resulting from the
above method, is an increasing function of the present day mass of the halo.
The mean value of varies from 0.0343 to 0.0484 for haloes with
present day masses in the range of to
. 2)The distribution of is close to
a log-normal, but, as it is already found in the results of N-body simulations,
the match is not satisfactory at the tails of the distribution. A new
analytical formula that approximates the results much more satisfactorily is
presented. 3) The distribution of the values of depends only weakly
on the redshift. 4) The spin parameter of an halo depends on the number of
recent major mergers. Specifically the spin parameter is an increasing function
of this number.Comment: 10 pages, 8 figure
Hypersurface-Invariant Approach to Cosmological Perturbations
Using Hamilton-Jacobi theory, we develop a formalism for solving
semi-classical cosmological perturbations which does not require an explicit
choice of time-hypersurface. The Hamilton-Jacobi equation for gravity
interacting with matter (either a scalar or dust field) is solved by making an
Ansatz which includes all terms quadratic in the spatial curvature.
Gravitational radiation and scalar perturbations are treated on an equal
footing. Our technique encompasses linear perturbation theory and it also
describes some mild nonlinear effects. As a concrete example of the method, we
compute the galaxy-galaxy correlation function as well as large-angle microwave
background fluctuations for power-law inflation, and we compare with recent
observations.Comment: 51 pages, Latex 2.09 ALBERTA THY/20-94, DAMTP R94/25 To appear in
Phys. Rev.
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