Microwave background anisotropies from gravitational waves: the 1 + 3 covariant approach

Challinor, A.

doi:10.1088/0264-9381/17/4/309

Cited by 81 publications

(155 citation statements)

References 42 publications

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“…where the time-dependent velocity is v ≡ q/ and is the comoving energy, and we follow the conventions of [12,41,42]. Here F without a subscript is the background distribution function, which is assumed to be Fermi-Dirac when the neutrinos are fully relativistic.…”

Section: Appendix A: Numerical Evolution Of Massive Neutrino Perturbamentioning

confidence: 99%

CMB power spectrum parameter degeneracies in the era of precision cosmology

Howlett

Lewis

Hall

et al. 2012

J. Cosmol. Astropart. Phys.

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459

371

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Cosmological parameter constraints from the CMB power spectra alone suffer several well-known degeneracies. These degeneracies can be broken by numerical artefacts and also a variety of physical effects that become quantitatively important with high-accuracy data e.g. from the Planck satellite. We study degeneracies in models with flat and non-flat spatial sections, non-trivial dark energy and massive neutrinos, and investigate the importance of various physical degeneracy-breaking effects. We test the camb power spectrum code for numerical accuracy, and demonstrate that the numerical calculations are accurate enough for degeneracies to be broken mainly by true physical effects (the integrated Sachs-Wolfe effect, CMB lensing and geometrical and other effects through recombination) rather than numerical artefacts. We quantify the impact of CMB lensing on the power spectra, which inevitably provides degeneracy-breaking information even without using information in the non-Gaussianity. Finally we check the numerical accuracy of sample-based parameter constraints using camb and CosmoMC. In an appendix we document recent changes to camb's numerical treatment of massive neutrino perturbations, which are tested along with other recent improvements by our degeneracy exploration results.

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Section: Appendix A: Numerical Evolution Of Massive Neutrino Perturbamentioning

confidence: 99%

CMB power spectrum parameter degeneracies in the era of precision cosmology

Howlett

Lewis

Hall

et al. 2012

J. Cosmol. Astropart. Phys.

Self Cite

459

371

View full text Add to dashboard Cite

show abstract

“…The mode-expanded 1+3 covariant equations describing the perturbations in the matter components other than the radiation, and the geometry, can be found in Refs. [5,9,10], so we need only consider the radiation here. Furthermore, we do not consider circular polarization any further since it is not generated by Thomson scattering.…”

Section: Scalar Perturbationsmentioning

confidence: 99%

“…Explicit forms for the tensor harmonics in the PSTF representation are given in the appendix; see also Ref. [10]. The tensor harmonics can be classified as having electric or magnetic parity.…”

Section: Tensor Perturbationsmentioning

confidence: 99%

“…[10]. Including polarization modifies the scattering source term, so that the integral solution becomes 13) in an open universe.…”

Section: (K)mentioning

confidence: 99%

“…In Ref. [10] we took φ k = (ν 2 + 3)E k /(ν 2 + 1) where E k is the initial amplitude of the dimensionless mode coefficient representing the electric part of the Weyl tensor. In this case, the minimal scaleinvariant prediction of one bubble open inflation is P φ = tanh(πν/2) [31].…”

Section: (K)mentioning

confidence: 99%

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Microwave background polarization in cosmological models

Challinor¹

2000

Phys. Rev. D

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130

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We introduce a new multipole formalism for polarized radiative transfer in general spacetime geometries. The polarization tensor is expanded in terms of coordinate-independent, projected symmetric trace-free (PSTF) tensorvalued multipoles. The PSTF representation allows us to discuss easily the observer dependence of the multipoles of the polarization, and to formulate the exact dynamics of the radiation in convenient 1+3 covariant form. For the case of an almost-Friedmann-Robertson-Walker (FRW) cosmological model we recast the Boltzmann equation for the polarization in to a hierarchy of multipole equations. This allows us to give a rigorous treatment of the generation and propagation of the polarization of the cosmic microwave background in almost-FRW models (with open, closed or flat geometries) without recourse to any harmonic decomposition of the perturbations. We also show how expanding the intensity and polarization multipoles in derivatives of harmonic functions gives a streamlined derivation of the mode-expanded multipole hierarchies. Integral solutions to these hierarchies are provided, and the relation of our formalism to others in the literature is discussed.

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Structure Formation in Modified Gravity Cosmologies

Barreira

2016

Springer Theses

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source• a link is made to the metadata record in Durham E-Theses• the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. AbstractWe study linear and nonlinear structure formation in cosmologies where the accelerated expansion is driven by modifications to general relativity (GR). We focus on Galileon andNonlocal gravity, which are two classes of models that have been attracting much attention.We derive the linearly perturbed model equations and solve them with suitably modified versions of Einstein-Boltzmann codes. We also derive the perturbed equations keeping the relevant nonlinear terms for small scale structure formation, which we solve using Nbody codes and semi-analytical techniques that were developed for these models. Using CMB, SNIa and BAO data we find strong evidence for nonzero active neutrino masses (Σm ν ≈ 0.6 eV) in all three main branches of covariant Galileon cosmologies, known as the Cubic, Quartic and Quintic models. However, in all branches, the lensing potential does not decay at late times on sub-horizon scales, which contradicts the measured positive sign of the ISW effect, thereby ruling out the Galileon model. The Nonlocal model we study should be able to fit the CMB with similar parameter values as ΛCDM. The N-body simulation results show that the covariant Galileon model admits realistic halo occupation distributions of luminous red galaxies, even for model parameters whose linear growth is noticieably enhanced (σ 8 ≈ 1) relative to ΛCDM. In the Cubic Galileon model the screening mechanism is very efficient on scales 1Mpc, but in the Quartic and Quintic sectors, as well as in the Nonlocal model, we identify potential tensions with Solar System bounds.We illustrate that, despite the direct modifications to the lensing potential in the CubicGalileon and Nonlocal models, cluster masses estimated from lensing remain the same as in GR. The lensing effects produced by cosmic voids found in the simulations of the Cubic Galileon are significanly boosted (≈ 100%) compared to GR, which strongly motivates using voids in tests of gravity. The combination of linear and nonlinear theory results presented here for Galileon and Nonlocal gravity is an example of what it could be done for any serious alternative models to ΛCDM, which will be tested by future experiments.

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Microwave background anisotropies from gravitational waves: the 1 + 3 covariant approach

Cited by 81 publications

References 42 publications

CMB power spectrum parameter degeneracies in the era of precision cosmology

CMB power spectrum parameter degeneracies in the era of precision cosmology

Microwave background polarization in cosmological models

Structure Formation in Modified Gravity Cosmologies

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