WMAP7 and future CMB constraints on annihilating dark matter: implications for GeV-scale WIMPs

Abstract

Aims. We calculate constraints from current and future cosmic microwave background (CMB) measurements on annihilating dark matter (DM) with masses below the electroweak scale: m DM = 5−100 GeV. In particular, we assume the S-wave annihilation mode to be dominant, and focus our attention on the lower end of this mass range, as DM particles with masses m DM ∼ 10 GeV have recently been claimed to be consistent with the CoGeNT and DAMA/LIBRA results, while also providing viable DM candidates to explain the measurements of Fermi and WMAP haze. We study the model (in)dependence of the CMB power spectra on particle physics DM models, large-scale structure formation and cosmological uncertainties. We attempt to find a simple and practical recipe for estimating current and future CMB bounds on a broad class of DM annihilation models. Methods. We use a model-independent description for DM annihilation into a wide set of Standard Model particles simulated by PYTHIA Monte Carlo. Our Markov chain Monte Carlo calculations used for finding model constraints involve realistic CMB likelihoods and assume a standard 6-parameter ΛCDM background cosmological model, which is extended by two additional DM annihilation parameters: m DM and σ A υ /m DM . Results. We show that in the studied DM mass range the CMB signal of DM annihilations is independent of the details of large-scale structure formation, distribution, and profile of DM halos and other cosmological uncertainties. All particle physics models of DM annihilation can be described with only one parameter, the fraction of energy carried away by neutrinos in DM annihilation. As the main result we provide a simple and rather generic fitting formula for calculating CMB constraints on the annihilation cross section of light WIMPs. We show that thermal relic DM in the CoGeNT, DAMA/LIBRA favored mass range is in a serious conflict with present CMB data for the annihilation channels with few neutrinos, and will definitely be tested by the Planck mission for all possible DM annihilation channels. Also, our findings strongly disfavor the claim that thermal relic DM annihilations with m DM ∼ 10 GeV and σ A υ ∼ 9 × 10 −25 cm 3 s −1 could be a cause of Fermi and WMAP haze.

General constraints on dark matter decay from the cosmic microwave background

“…Using these results, [20] studied the impact on the CMB anisotropy spectrum of keV − TeV photons and e + e − pairs produced by DM annihilation. Extending earlier studies [21][22][23], that work demonstrated that the imprint on the CMB anisotropy spectrum was essentially identical for all models of s-wave DM annihilation with keV − TeV annihilation products, up to an overall model-dependent scaling factor, which could be estimated using principal component analysis (PCA). [20] further provided a simple recipe for determining the CMB anisotropy constraints on arbitrary models of annihilating DM: compute the spectrum of electrons, positrons and photons produced by a single annihilation, determine the weighted efficiency factor using the results of [20], and then apply the bound computed by the Planck collaboration on the product of this efficiency factor and the DM annihilation cross section.…”

Planck2013 results. XVI. Cosmological parameters

“…As recently shown in several papers (see e.g., Galli et al 2009Galli et al , 2011Giesen et al 2012;Hutsi et al 2011;Natarajan 2012;Evoli et al 2013) CMB anisotropies offer an opportunity to constrain DM annihilation models.…”

“…(97), the factor f (z) depends on the details of the annihilation process, such as the mass of the DM particle and the annihilation channel (see e.g., Slatyer et al 2009). The functional shape of f (z) can be taken into account using generalized parameterizations (Finkbeiner et al 2012;Hutsi et al 2011). However, as shown in Galli et al (2011), Giesen et al (2012), and Finkbeiner et al (2012 it is possible to neglect the redshift dependence of f (z) to first approximation, since current data shows very little sensitivity to variations of this function.…”

Searching for dark matter in the CMB: A compact parametrization of energy injection from new physics

“…While this enhancement would not be significant during freezeout, it would be effective at recombination when the typical velocity of dark matter is v ∼ 10 −8 c [9]. With the release of data from Planck expected in the next two years, models falling into these categories should either be robustly ruled out, or give rise to a measurable signal [9,10,13]. If no signal is observed, the sensitivity of Planck will allow us to probe regions of parameter space relevant for supersymmetric models, where the DM is a thermal relic with mass of several tens of GeV.…”