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On the density of Cold Dark Matter

A. Melchiorri, J. Silk

TL;DR

The study tackles constraining the CDM density and rms fluctuations by jointly analyzing CMB data from multiple experiments with large-scale structure priors, testing robustness to extensions like quintessence and extra relativistic species. It adopts a grid-based six-parameter CDM framework and marginalizes nuisance parameters, finding $\Omega_{cdm}h^2$ around $0.11$–$0.12$, $n_S$ near $0.93$, and $\sigma_8^*$ around $0.66$ (95% CL). These results persist across model variations and align with lensing constraints on sub-galactic scales, reinforcing the case for non-baryonic CDM. Potential tension would only arise if external data converge on much higher $\sigma_8$, but current analyses favor consistency with $\Lambda$CDM.

Abstract

The nature of dark matter is increasingly constrained by cosmological data. In this paper, we examine the implications of the Cosmic Microwave Background anisotropy limits on the density of cold dark matter under different theoretical assumptions and combinations of datasets. We infer the constraint $Ω_{cdm}h^2=0.12\pm0.04$ (at 95% c.l.). The CDM models are compared with the shape of the linear matter power spectrum inferred from the 2dF galaxy redshift survey and with the rms mass fluctuations from recent local cluster observations. We found that a value of $σ_8 \sim 1$ as suggested by recent cosmic shear data is not favoured by the CMB data alone nor by combined CMB+SN-Ia, CMB+HST or CMB+2dFGRS analyses. We also extrapolate our bounds on the rms linear mass fluctuations to sub-galactic scales and compare them with recent lensing constraints, finding agreement with the standard $Λ$CDM model.

On the density of Cold Dark Matter

TL;DR

The study tackles constraining the CDM density and rms fluctuations by jointly analyzing CMB data from multiple experiments with large-scale structure priors, testing robustness to extensions like quintessence and extra relativistic species. It adopts a grid-based six-parameter CDM framework and marginalizes nuisance parameters, finding around –, near , and around (95% CL). These results persist across model variations and align with lensing constraints on sub-galactic scales, reinforcing the case for non-baryonic CDM. Potential tension would only arise if external data converge on much higher , but current analyses favor consistency with CDM.

Abstract

The nature of dark matter is increasingly constrained by cosmological data. In this paper, we examine the implications of the Cosmic Microwave Background anisotropy limits on the density of cold dark matter under different theoretical assumptions and combinations of datasets. We infer the constraint (at 95% c.l.). The CDM models are compared with the shape of the linear matter power spectrum inferred from the 2dF galaxy redshift survey and with the rms mass fluctuations from recent local cluster observations. We found that a value of as suggested by recent cosmic shear data is not favoured by the CMB data alone nor by combined CMB+SN-Ia, CMB+HST or CMB+2dFGRS analyses. We also extrapolate our bounds on the rms linear mass fluctuations to sub-galactic scales and compare them with recent lensing constraints, finding agreement with the standard CDM model.

Paper Structure

This paper contains 6 sections, 1 equation, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Cosmological Constraints on CDM
  3. Method
  4. CMB results and test for theoretical assumptions.
  5. Comparison with complementary datasets.
  6. Discussion

Figures (4)

  • Figure 1: Top panel: CMB anisotropies and CDM. Bottom panel: Allowed region for the matter power spectrum from CMB and from other cosmological observables obtained under the assumption of adiabatic CDM primordial fluctuations. The data from the 2dF redshift survey (Tegmark and Hamilton, 2002) is also plotted in the figure.
  • Figure 2: Constraints in the $(\Omega_m)^{0.6}\sigma_8-\Omega_{cdm}h^2$ plane. The results of the $3$ combined analysis CMB+HST, CMB+SN-Ia and CMB+2dFGRS are shown together with the $68 \%$ c.l. cluster constraints
  • Figure 3: Constraints in the $\Omega_m-\sigma_8$ plane. The results of the $3$ combined analysis CMB+HST, CMB+SN-Ia and CMB+2dFGRS are shown together with the $68 \%$ c.l. constraints from Viana et al. 2001 and Pierpaoli et al 2001.
  • Figure 4: The predictions of the CDM models that are within the $95 \%$ CMB constraints in the $\sigma(R)-R$ plane together with a region indicative of the constraint obtained from lensing.