286 research outputs found
The CMBR Spectrum
A short review of the measured spectrum of the Cosmic Microwave Background
Radiation (CMBR) and implications. Extensions of the Kompaneets equation and
Sunyaev-Zel'dovich effect are given.Comment: 30 pages, 9 figures from lectures at NATO ASI "The Cosmic Microwave
Background" Strasbourg 199
Confirmation of the Copernican principle at Gpc radial scale and above from the kinetic Sunyaev Zel'dovich effect power spectrum
The Copernican principle, a cornerstone of modern cosmology, remains largely
unproven at Gpc radial scale and above. Here we will show that, violations of
this type will inevitably cause a first order anisotropic kinetic Sunyaev
Zel'dovich (kSZ) effect. If large scale radial inhomogeneities have amplitude
large enough to explain the "dark energy" phenomena, the induced kSZ power
spectrum will be much larger than the ACT/SPT upper limit. This single test
confirms the Copernican principle and rules out the adiabatic void model as a
viable alternative to dark energy.Comment: 4 pages, 2 figures. v2: updated with ACT result. v3: updated with SPT
result. Expanded discussions. Accepted to PR
Perturbations from cosmic strings in cold dark matter
A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed
Perturbations from strings don't look like strings!
A systematic analysis is challenging popular ideas about perturbation from cosmic strings. One way in which the picture has changed is reviewed. It is concluded that, while the scaling properties of cosmic strings figure significantly in the analysis, care must be taken when thinking in terms of single time snapshots. The process of seeding density perturbations is not fundamentally localized in time, and this fact can wash out many of the details which appear in a single snapshot
Cold + Hot Dark Matter and the Cosmic Microwave Background
We examine the cosmic microwave background power spectrum for adiabatic
models with a massive neutrino component. We present the results of a detailed
numerical evolution of cold + hot dark matter (CHDM) models and compare with
the standard cold dark matter (CDM) spectrum. The difference is of order
for for currently popular CHDM models. With
semi-analytic approximations, we also discuss the relevant physics involved.
Finally we remark on the ability of future experiments to differentiate between
these models. An all-sky experiment with a beam size smaller than 30 arcminutes
can distinguish between CHDM and CDM if other cosmological parameters are
known. Even allowing other parameters to vary, it may be possible to
distinguish CDM from CHDM.Comment: Compressed uuencoded postscript, 26 pages including figures. Color
version available at http://www-astro-theory.fnal.gov
Generation of Isocurvature from Curvature Inhomogeneities on Super-Horizon Scales
Here it is shown 1) how isocurvature inhomogeneities correlated on causally
disconnected (super-horizon) scales are generated from curvature
inhomogeneities which are known to be correlated on these scales 2) that
super-horizon isocurvature generation is nearly inevitable for non-equilibrium
chemical processes 3) that the amplitude of the compositional isocurvature
correlations a) can be large for production of rare objects, b) falls off
rapidly with separation c) falls off at scales below the horizon when these
modes are generated. These two fall-offs results in an "isocurvature bump" in
the power spectrum. Isocurvature generation is illustrated by the process of
dark matter freeze-in, computed here with both separate universe modelling and
linear perturbation theory. For freeze-in the most prominent isocurvature modes
are inhomogeneities in the ratio of dark matter to standard model matter. Much
smaller inhomogeneities in the ratio of baryons to standard model entropy are
also produced. Previous constraints on freeze-in from Ly- clouds limit
the bump enhancement to on comoving scales Mpc.
Current observations are not sensitive to the isocurvature modes generated in
viable freeze-in models. Results are obtained using a somewhat novel framework
to describe cosmological inhomogeneities.Comment: 22 pages 2 figures. Composed as Mathematica notebook. Will be
migrated to LaTeX in future version
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