Constraints on leptonically annihilating dark matter from reionization and extragalactic gamma background

Abstract

Context. The PAMELA, Fermi and HESS experiments (PFH) have shown anomalous excesses in the cosmic positron and electron fluxes. A very exciting possibility is that those excesses are due to annihilating dark matter (DM). Aims. In this paper we calculate constraints on leptonically annihilating DM using observational data on diffuse extragalactic γ-ray background and measurements of the optical depth to the last-scattering surface, and compare those with the PFH favored region in the m DM − σ A υ plane. Methods. Having specified the detailed form of the energy input with PYTHIA Monte Carlo tools we solve the radiative transfer equation which allows us to determine the amount of energy being absorbed by the cosmic medium and also the amount left over for the diffuse gamma background. Results. We find that the constraints from the optical depth measurements are able to rule out the PFH favored region fully for the τ − + τ + annihilation channel and almost fully for the μ − + μ + annihilation channel. It turns out that those constraints are quite robust with almost no dependence on low redshift clustering boost. The constraints from the γ-ray background are sensitive to the assumed halo concentration model and, for the power law model, rule out the PFH favored region for all leptonic annihilation channels. We also find that it is possible to have models that fully ionize the Universe at low redshifts. However, those models produce too large free electron fractions at z 100 and are in conflict with the optical depth measurements. Also, the magnitude of the annihilation cross-section in those cases is larger than suggested by the PFH data.

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

“…Even though most of these analyses have assumed a simple "on the spot" approximation for the energy deposition 1 , more recent studies Hütsi et al 2009) followed the energy transport problem including various energy-loss mechanisms in a more realistic way. Compared to the analysis of Slatyer et al (2009), which partially relies on the 1 I.e., energy input from DM annihilations is assumed to get instantaneously absorbed by the cosmic medium, with some efficiency factor f .…”

The Redshift Evolution of LCDM Halo Parameters

“…The properties of dark matter haloes can be characterized with several different parameters, one of the most important ones is the concentration parameter which accounts for the shape of the mass density profile and therefore has important implications in determining the properties of the galaxies forming inside [12], as well as it has direct influence in the flux of radiation produced during the annihilation process of dark matter in the center of the halo [7]. Previous works have been addressed in the study of the structure of dark matter haloes.…”

Leptonic dark matter annihilation in the evolving universe: constraints and implications

“…The implications for the DM models from the above effects on the CMB were discussed recently in [38,58]. Since these effects are not sensitive to the clumpiness factor ∆ 2 (z), we will not discuss them in detail here.…”

“…associated with the annihilation process itself. The γ-ray flux observed at redshift z is obtained by integrating the emissivity through evolution history of the universe [38,46],…”