536 research outputs found
Cosmic Microwave Background Anisotropies from Scaling Seeds: Fit to Observational Data
We compute cosmic microwave background angular power spectra for scaling seed
models of structure formation. A generic parameterization of the energy
momentum tensor of the seeds is employed. We concentrate on two regions of
parameter space inspired by global topological defects: O(4) texture models and
the large-N limit of O(N) models. We use fitting to compare these
models to recent flat-band power measurements of the cosmic microwave
background. Only scalar perturbations are considered.Comment: LaTeX file 4 pages, 4 postscript figs. revised version, to appear in
PR
Constraints on the neutrino mass and the cosmological constant from large scale structure observations
The observational data on the large scale structure (LSS) of the Universe are
used to establish the upper limit on the neutrino content marginalized over all
other cosmological parameters within the class of adiabatic inflationary
models. It is shown that the upper 2 limit on the neutrino content can
be expressed in the form or, via the
neutrino mass, eV.Comment: 5 pages, to appear in the proceedings of the CAPP2000 Conference,
Verbier, Switzerland, July, 200
Do the cosmological observational data prefer phantom dark energy?
The dynamics of expansion and large scale structure formation of the Universe
are analyzed for models with dark energy in the form of a phantom scalar field
which initially mimics a -term and evolves slowly to the Big Rip
singularity. The discussed model of dark energy has three parameters -- the
density and the equation of state parameter at the current epoch,
and , and the asymptotic value of the equation of state parameter at
, . Their best-fit values are determined jointly
with all other cosmological parameters by the MCMC method using observational
data on CMB anisotropies and polarization, SNe Ia luminosity distances, BAO
measurements and more. Similar computations are carried out for CDM
and a quintessence scalar field model of dark energy. It is shown that the
current data slightly prefer the phantom model, but the differences in the
maximum likelihoods are not statistically significant. It is also shown that
the phantom dark energy with monotonically increasing density in future will
cause the decay of large scale linear matter density perturbations due to the
gravitational domination of dark energy perturbations long before the Big Rip
singularity.Comment: 13 pages, 8 figures, 5 tables; comments and references added; version
accepted for publication in Phys.Rev.
Cosmological parameters from complementary observations of the Universe
We use observational data on the large-scale structure (LSS) of the Universe measured over a wide range of scales, from subgalactic up to horizon scale, and on the cosmic microwave background anisotropies to determine cosmological parameters within the class of adiabatic inflationary models. We show that a mixed dark matter model with cosmological constant (ΛMDM model) and parameters Ωm = 0.37−0.15+0.25,ΩΛ = 0.69−0.20+0.15,Ω = 0.03−0.03+0.07,N = 1,Ωb = 0.037−0.018+0.033,ns = 1.02−0.10+0.09,h = 0.71−0.19+0.22,bcl = 2.4−0.7+0.7 (1σ confidence limits) matches observational data on LSS, the nucleosynthesis constraint, direct measurements of the Hubble constant, the high-redshift supernova type Ia results and the recent measurements of the location and amplitude of the first acoustic peak in the cosmic microwave background (CMB) anisotropy power spectrum. The best model is Λ-dominated (65 per cent of the total energy density) and has slightly positive curvature, Ω = 1.06. The clustered matter consists of 8 per cent massive neutrinos, 10 per cent baryons and 82 per cent cold dark matter (CDM). The upper 2σ limit on the neutrino content can be expressed in the form Ωh2 = N0.64≤0.042 or, via the neutrino mass, m≤4.0 eV. The upper 1(2)σ limit for the contribution of a tensor mode to the COBE DMR data is TS<1(1.5). Furthermore, it is shown that the LSS observations, together with the Boomerang (+MAXIMA-1) data on the first acoustic peak, rule out zero-Λ models at more than a 2σ confidence limi
Acoustic peaks and dips in the CMB power spectrum: observational data and cosmological constraints
The locations and amplitudes of three acoustic peaks and two dips in the last
releases of the Boomerang, MAXIMA and DASI measurements of the cosmic microwave
background (CMB) anisotropy power spectra as well as their statistical
confidence levels are determined in a model-independent way. It is shown that
the Boomerang-2001 data (Netterfield et al. 2001) fixes the location and
amplitude of the first acoustic peak at more than 3\sigma confidence level. The
next two peaks and dips are determined at a confidence level above 1\sigma but
below 2\sigma. The locations and amplitudes of the first three peaks and two
dips are 212+/-17, 5426+/-1218\mu K^2, 544+/-56, 2266+/-607\mu K^2, 843+/-35,
2077+/-876\mu K^2, 413+/-50, 1960+/-503\mu K^2, 746+/-89, 1605+/-650\mu K^2
respectively (1\sigma errors include statistical and systematic errors). The
MAXIMA and DASI experiments give similar values for the extrema which they
determine. The determined cosmological parameters from the CMB acoustic extrema
data show good agreement with other determinations, especially with the baryon
content as deduced from standard nucleosynthesis constraints. These data
supplemented by the constraints from direct measurements of some cosmological
parameters and data on large scale structure lead to a best-fit model which
agrees with practically all the used experimental data within 1\sigma. The
best-fit parameters are: \Omega_{\Lambda}=0.64^{+0.14}_{-0.27}, \Omega_{m}=
0.36^{+0.21}_{-0.11}, \Omega_b=0.047^{+0.093}_{-0.024},
n_s=1.0^{+0.59}_{-0.17}, h=0.65^{+0.35}_{-0.27} and \tau_c=0.15^{+0.95}_{-0.15}
(plus/minus values show 1\sigma upper/lower limits obtained by marginalization
over all other model parameters). The best-fit values of \Omega_{\nu} and T/S
are close to zero, their 1\sigma upper limits are 0.17 and 1.7 respectively.Comment: 34 pages, 10 figures; accepted by ApJ; some corrections in the text
are made and a few references are adde
Cosmological parameters from complementary observations of the Universe
We use observational data on the large scale structure (LSS) of the Universe
measured over a wide range of scales from sub-galactic up to horizon scale and
on the cosmic microwave background anisotropies to determine cosmological
parameters within the class of adiabatic inflationary models. We show that a
mixed dark matter model with cosmological constant (MDM model) and
parameters ,
, ,
, , ,
, (1 confidence
limits) matches observational data on LSS, the nucleosynthesis constraint,
direct measurements of Hubble constant, the high redshift supernova type Ia
results and the recent measurements of the location and amplitude of the first
acoustic peak in the CMB anisotropy power spectrum. The best model is
dominated (65% of the total energy density) and has slightly positive
curvature, . The clustered matter consists in 8% massive
neutrinos, 10% baryons and 82% cold dark matter (CDM). The upper 2
limit on the neutrino content can be expressed in the form
or, via the neutrino mass,
eV. The upper 1(2) limit for the contribution of a
tensor mode to the COBE DMR data is T/S. Furthermore, it is shown that
the LSS observations together with the Boomerang (+MAXIMA-1) data on the first
acoustic peak rule out zero- models at more than confidence
limit.Comment: 13 pages, 3 figures; accepted by MNRAS; minor corrections in the
text, a few references are adde
The Cosmic Microwave Background and Helical Magnetic Fields: the tensor mode
We study the effect of a possible helicity component of a primordial magnetic
field on the tensor part of the cosmic microwave background temperature
anisotropies and polarization. We give analytical approximations for the tensor
contributions induced by helicity, discussing their amplitude and spectral
index in dependence of the power spectrum of the primordial magnetic field. We
find that an helical magnetic field creates a parity odd component of gravity
waves inducing parity odd polarization signals. However, only if the magnetic
field is close to scale invariant and if its helical part is close to maximal,
the effect is sufficiently large to be observable. We also discuss the
implications of causality on the magnetic field spectrum.Comment: We have corrected a normalisation error which was pointed out to us
by Antony Lewis. It enhances our limits on the magnetic fields by
(2\pi)^{3/4} ~
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