1,130 research outputs found
The Cosmic Linear Anisotropy Solving System (CLASS) III: Comparision with CAMB for LambdaCDM
By confronting the two independent Boltzmann codes CLASS and CAMB, we
establish that for concordance cosmology and for a given recombination history,
lensed CMB and matter power spectra can be computed by current codes with an
accuracy of 0.01%. We list a few tiny changes in CAMB which are necessary in
order to reach such a level. Using the common limit of the two codes as a set
of reference spectra, we derive precision settings corresponding to fixed
levels of error in the computation of a CMB likelihood. We find that for a
given precision level, CLASS is about 2.5 times faster than CAMB for computing
the lensed CMB spectra of a LambdaCDM model. The nature of the main
improvements in CLASS (which may each contribute to these performances) is
discussed in companion papers.Comment: 16 pages, 4 figures, 1 table. Typos corrected, comparison extended to
lower precision settings. Code available at http://class-code.ne
TASI Lectures on Cosmological Perturbations
We present a self-contained summary of the theory of linear cosmological
perturbations. We emphasize the effect of the six parameters of the minimal
cosmological model, first, on the spectrum of Cosmic Microwave Background
temperature anisotropies, and second, on the linear matter power spectrum. We
briefly review at the end the possible impact of a few non-minimal dark matter
and dark energy models.Comment: TASI 2013 lecture note
Double D-term inflation
Comparisons of cosmological models to current data show that the presence of
a non-trivial feature in the primordial power spectrum of fluctuations, around
the scale k=0.05 h/Mpc, is an open and exciting possibility, testable in a near
future. This could set new constraints on inflationary models. In particular,
current data favour a Lambda-CDM model with a steplike spectrum, and more power
on small scales. So far, this possibility has been implemented only in toy
models of inflation. In this work, we propose a supersymmetric model with two
U(1) gauge symmetries, associated with two Fayet-Iliopoulos terms. Partial
cancellation of the Fayet-Iliopoulos by one of the charged fields generates a
step in the primordial power spectrum of adiabatic perturbations. We show that
when this field if charged under both symmetries, the spectrum may have more
power on small scales.Comment: 13 pages, revised version accepted for publication in Phys. Lett.
The Cosmic Linear Anisotropy Solving System (CLASS) I: Overview
The Cosmic Linear Anisotropy Solving System (CLASS) is a new accurate
Boltzmann code, designed to offer a more user-friendly and flexible coding
environment to cosmologists. CLASS is very structured, easy to modify, and
offers a rigorous way to control the accuracy of output quantities. It is also
incidentally a bit faster than other codes. In this overview, we present the
general principles of CLASS and its basic structure. We insist on the
friendliness and flexibility aspects, while accuracy, physical approximations
and performances are discussed in a series of companion papers.Comment: 19 pages, typos corrected. Code available at http://class-code.ne
Optimal polarisation equations in FLRW universes
This paper presents the linearised Boltzmann equation for photons for scalar,
vector and tensor perturbations in flat, open and closed FLRW cosmologies. We
show that E- and B-mode polarisation for all types can be computed using only a
single hierarchy. This was previously shown explicitly for tensor modes in flat
cosmologies but not for vectors, and not for non-flat cosmologies.Comment: 27 pages, prepared for submission to JCAP. Matches published versio
Non-linear matter power spectrum from Time Renormalisation Group: efficient computation and comparison with one-loop
We address the issue of computing the non-linear matter power spectrum on
mildly non-linear scales with efficient semi-analytic methods. We implemented
M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop
(D1L) limit in a numerical module for the new Boltzmann code CLASS. Our
publicly released module is valid for LCDM models, and optimized in such a way
to run in less than a minute for D1L, or in one hour (divided by number of
nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop
approaches reveals that results depend crucially on the assumed initial
bispectrum at high redshift. When starting from a common assumption, the three
methods give roughly the same results, showing that the partial resumation of
diagrams beyond one loop in the TRG method improves one-loop results by a
negligible amount. A comparison with highly accurate simulations by M. Sato &
T. Matsubara shows that all three methods tend to over-predict non-linear
corrections by the same amount on small wavelengths. Percent precision is
achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1.Comment: 24 pages, 7 figures, revised title and conclusions, version accepted
in JCAP, code available at http://class-code.ne
Massive neutrinos and cosmology
The present experimental results on neutrino flavour oscillations provide
evidence for non-zero neutrino masses, but give no hint on their absolute mass
scale, which is the target of beta decay and neutrinoless double-beta decay
experiments. Crucial complementary information on neutrino masses can be
obtained from the analysis of data on cosmological observables, such as the
anisotropies of the cosmic microwave background or the distribution of
large-scale structure. In this review we describe in detail how free-streaming
massive neutrinos affect the evolution of cosmological perturbations. We
summarize the current bounds on the sum of neutrino masses that can be derived
from various combinations of cosmological data, including the most recent
analysis by the WMAP team. We also discuss how future cosmological experiments
are expected to be sensitive to neutrino masses well into the sub-eV range.Comment: 122 pages, 23 figures, misprints corrected and references added.
Review article to be published in Physics Report
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