Evolution of cosmological dark matter perturbations

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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“…a truncated fluid hierarchy); this is described in detail in Ref. [42] and was previously implemented in camb.…”

Section: Discussionmentioning

confidence: 99%

“…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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438

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“…We adopt the covariant multipole perturbation approach for the massive neutrino (Ma & Bertschinger 1995;Lewis & Challinor 2002). We replace the Fermi-Dirac distribution of the massive neutrino by the momentum distributions of the WDM models discussed above.…”

Section: Linear Matter Power Spectra and Normalized Velocity Distribumentioning

confidence: 99%

Structure of dark matter halos in warm dark matter models and in models with long-lived charged massive particles

Kamada

Yoshida

Kohri

et al. 2013

J. Cosmol. Astropart. Phys.

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We study the formation of non-linear structures in Warm Dark Matter (WDM) models and in a Long-Lived Charged Massive Particle (CHAMP) model. CHAMPs with a decay lifetime of about 1 yr induce characteristic suppression in the matter power spectrum at subgalactic scales through acoustic oscillations in the thermal background. We explore structure formation in such a model. We also study three WDM models, where the dark matter particles are produced through the following mechanisms: i) WDM particles are produced in the thermal background and then kinematically decoupled; ii) WDM particles are fermions produced by the decay of thermal heavy bosons; and iii) WDM particles are produced by the decay of non-relativistic heavy particles. We show that the linear matter power spectra for the three models are all characterised by the comoving Jeans scale at the matter-radiation equality. Furthermore, we can also describe the linear matter power spectrum for the Long-Lived CHAMP model in terms of a suitably defined characteristic cut-off scale k Ch , similarly to the WDM models. We perform large cosmological N -body simulations to study the non-linear growth of structures in these four models. We compare the halo mass functions, the subhalo mass functions, and the radial distributions of subhalos in simulated Milky Way-size halos. For the characteristic cut-off scale k cut = 51 h Mpc −1 , the subhalo abundance -2 -(∼ 10 9 M sun ) is suppressed by a factor of ∼ 10 compared with the standard ΛCDM model. We then study the models with k cut ≃ 51, 410, 820 h Mpc −1 , and confirm that the halo and the subhalo abundances and the radial distributions of subhalos are indeed similar between the different WDM models and the Long-Lived CHAMP model. The result suggests that the cut-off scale k cut not only characterises the linear power spectra but also can be used to predict the non-linear clustering properties. The radial distribution of subhalos in Milky Way-size halos is consistent with the observed distribution for k cut ∼ 50 − 800 h Mpc −1 ; such models resolve the so-called "missing satellite problem".

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“…I use the approach of the covariant multipole perturbation evolution equations for massive neutrinos in Ref. [60] and implemented in the Code for Anisotropies in the Microwave Background (CAMB) [61]. The multipole equations depend on the value of the massive neutrino energy distribution and its momentum derivative, but I will not reproduce them here.…”

Section: Perturbation Evolutionmentioning

confidence: 99%

Production and evolution of perturbations of sterile neutrino dark matter

2006

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Sterile neutrinos, fermions with no standard model couplings [SU(2) singlets], are predicted by most extensions of the standard model, and may be the dark matter. I describe the nonthermal production and linear perturbation evolution in the early universe of this dark matter candidate. I calculate production of sterile neutrino dark matter including effects of Friedmann dynamics dictated by the quark-hadron transition and particle population, the alteration of finite temperature effective mass of active neutrinos due to the presence of thermal leptons, and heating of the coupled species due to the disappearance of degrees of freedom in the plasma. These effects leave the sterile neutrinos with a non-trivial momentum distribution. I also calculate the evolution of sterile neutrino density perturbations in the early universe through the linear regime and provide a fitting function form for the transfer function describing the suppression of small scale fluctuations for this warm dark matter candidate. The results presented here differ quantitatively from previous work due to the inclusion here of the relevant physical effects during the production epoch.

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Evolution of cosmological dark matter perturbations

Cited by 634 publications

References 16 publications

CMB power spectrum parameter degeneracies in the era of precision cosmology

CMB power spectrum parameter degeneracies in the era of precision cosmology

Structure of dark matter halos in warm dark matter models and in models with long-lived charged massive particles

Production and evolution of perturbations of sterile neutrino dark matter

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