30 research outputs found
Steps toward the power spectrum of matter. III. The primordial spectrum
Observed power spectrum of matter found in Papers I and II is compared with
analytical power spectra. Spatially flat cold and mixed dark matter models with
cosmological constant and open models are considered. The primordial power
spectrum of matter is determined using the power spectrum of matter and the
transfer functions of analytical models. The primordial power spectrum has a
break in amplitude. We conclude that a scale-free primordial power spectrum is
excluded if presently available data on the distribution of clusters and
galaxies represent the true mass distribution of the Universe.Comment: LaTex (sty files added), 22 pages, 5 PostScript figures embedded,
Astrophysical Journal (accepted
Power Spectra for Cold Dark Matter and its Variants
The bulk of recent cosmological research has focused on the adiabatic cold
dark matter model and its simple extensions. Here we present an accurate
fitting formula that describes the matter transfer functions of all common
variants, including mixed dark matter models. The result is a function of
wavenumber, time, and six cosmological parameters: the massive neutrino
density, number of neutrino species degenerate in mass, baryon density, Hubble
constant, cosmological constant, and spatial curvature. We show how
observational constraints---e.g. the shape of the power spectrum, the abundance
of clusters and damped Lyman-alpha systems, and the properties of the
Lyman-alpha forest--- can be extended to a wide range of cosmologies, including
variations in the neutrino and baryon fractions in both high-density and
low-density universes.Comment: 20 pages, LaTeX, 4 figures. Submitted to ApJ. Electronic versions of
the fitting formula, as well as simple codes to output cosmological
quantities (e.g. sigma_8) as a function of parameters and illustrative
animations of parameter dependence, are available at
http://www.sns.ias.edu/~whu/transfer/transfer.htm
Contractions of Low-Dimensional Lie Algebras
Theoretical background of continuous contractions of finite-dimensional Lie
algebras is rigorously formulated and developed. In particular, known necessary
criteria of contractions are collected and new criteria are proposed. A number
of requisite invariant and semi-invariant quantities are calculated for wide
classes of Lie algebras including all low-dimensional Lie algebras.
An algorithm that allows one to handle one-parametric contractions is
presented and applied to low-dimensional Lie algebras. As a result, all
one-parametric continuous contractions for the both complex and real Lie
algebras of dimensions not greater than four are constructed with intensive
usage of necessary criteria of contractions and with studying correspondence
between real and complex cases.
Levels and co-levels of low-dimensional Lie algebras are discussed in detail.
Properties of multi-parametric and repeated contractions are also investigated.Comment: 47 pages, 4 figures, revised versio
A built-in scale in the initial spectrum of density perturbations: evidence from cluster and CMB data
We calculate temperature anisotropies of the cosmic microwave background
(CMB) for several initial power spectra of density perturbations with a
built-in scale suggested by recent optical data on the spatial distribution of
rich clusters of galaxies. Using cosmological models with different values of
spectral index, baryon fraction, Hubble constant and cosmological constant, we
compare the calculated radiation power spectrum with the CMB temperature
anisotropies measured by the Saskatoon experiment. We show that spectra with a
sharp peak at 120 h^{-1} Mpc are in agreement with the Saskatoon data. The
combined evidence from cluster and CMB data favours the presence of a peak and
a subsequent break in the initial matter power spectrum. Such feature is
similar to the prediction of an inflationary model where an inflaton field is
evolving through a kink in the potential.Comment: LaTex style, 9 pages, 3 PostScript figures embedded, accepted by J.
Exper. Theor. Phy
The Formation of Cosmic Structures in a Light Gravitino Dominated Universe
We analyse the formation of cosmic structures in models where the dark matter
is dominated by light gravitinos with mass of eV -- 1 keV, as predicted
by gauge-mediated supersymmetry (SUSY) breaking models. After evaluating the
number of degrees of freedom at the gravitinos decoupling (), we compute
the transfer function for matter fluctuations and show that gravitinos behave
like warm dark matter (WDM) with free-streaming scale comparable to the galaxy
mass scale. We consider different low-density variants of the WDM model, both
with and without cosmological constant, and compare the predictions on the
abundances of neutral hydrogen within high-redshift damped Ly-- systems
and on the number density of local galaxy clusters with the corresponding
observational constraints. We find that none of the models satisfies both
constraints at the same time, unless a rather small value (\mincir
0.4) and a rather large Hubble parameter (\magcir 0.9) is assumed.
Furthermore, in a model with warm + hot dark matter, with hot component
provided by massive neutrinos, the strong suppression of fluctuation on scales
of \sim 1\hm precludes the formation of high-redshift objects, when the
low-- cluster abundance is required. We conclude that all different variants
of a light gravitino DM dominated model show strong difficulties for what
concerns cosmic structure formation.
This gives a severe cosmological constraint on the gauge-mediated SUSY
breaking scheme.Comment: 28 pages,Latex, submitted for publication to Phys.Rev.
Large Scale Structure and Supersymmetric Inflation without Fine Tuning
We explore constraints on the spectral index of density fluctuations and
the neutrino energy density fraction , employing data from a
variety of large scale observations. The best fits occur for and
, over a range of Hubble constants km
s Mpc. We present a new class of inflationary models based on
realistic supersymmetric grand unified theories which do not have the usual
`fine tuning' problems. The amplitude of primordial density fluctuations, in
particular, is found to be proportional to , where
denote the GUT (Planck) scale, which is reminiscent of cosmic strings! The
spectral index , in excellent agreement with the observations
provided the dark matter is a mixture of `cold' and `hot' components.Comment: LaTEX, 14 pp. + 1 postscript figure appende
Reconstructing the Inflaton Potential --- an Overview
We review the relation between the inflationary potential and the spectra of
density (scalar) perturbations and gravitational waves (tensor perturbations)
produced, with particular emphasis on the possibility of reconstructing the
inflaton potential from observations. The spectra provide a potentially
powerful test of the inflationary hypothesis; they are not independent but
instead are linked by consistency relations reflecting their origin from a
single inflationary potential. To lowest-order in a perturbation expansion
there is a single, now familiar, relation between the tensor spectral index and
the relative amplitude of the spectra. We demonstrate that there is an infinite
hierarchy of such consistency equations, though observational difficulties
suggest only the first is ever likely to be useful. We also note that since
observations are expected to yield much better information on the scalars than
on the tensors, it is likely to be the next-order version of this consistency
equation which will be appropriate, not the lowest-order one. If inflation
passes the consistency test, one can then confidently use the remaining
observational information to constrain the inflationary potential, and we
survey the general perturbative scheme for carrying out this procedure.
Explicit expressions valid to next-lowest order in the expansion are presented.
We then briefly assess the prospects for future observations reaching the
quality required, and consider a simulated data set that is motivated by this
outlook.Comment: 69 pages standard LaTeX plus 4 postscript figures. Postscript version
of text in landscape format (35 pages) available at
http://star-www.maps.susx.ac.uk/papers/infcos_papers.html Modifications are a
variety of updates to discussion and reference