Galactic signatures of decaying dark matter

Abstract

If dark matter decays into electrons and positrons, it can affect Galactic radio emissions and the local cosmic ray fluxes. We propose a new, more general analysis of constraints on dark matter. The constraints can be obtained for any decaying dark matter model by convolving the specific dark matter decay spectrum with a response function. We derive this response function from full-sky radio surveys at 408 MHz, 1.42 GHz and 23 GHz, as well as from the positron flux recently reported by PAMELA. We discuss the influence of astrophysical uncertainties on the response function, such as from propagation and from the profiles of the dark matter and the Galactic magnetic field. As an application, we find that some widely used dark matter decay scenarios can be ruled out under modest assumptions.

Lifetime constraints for late dark matter decay

“…Because of the Galactic magnetic field, charged particles are largely expected to follow the magnetic lines and converge toward the GC, as long as their Larmor radius, r L = γm/qB, is much smaller than the scale of variation of the magnetic field. In the Milky Way, B few µG, and (d ln B/dr) −1 ∼ few kpc [5]. Positrons are thus expected to follow the magnetic lines, even for energies much higher than the ones considered in this analysis.…”

“…Here, we use the response functions derived in Ref. [5] for synchrotron radiation, and in Ref. [6] for IC and bremsstrahlung emission, to obtain constraints for the χ → χ ′ + e ± decay process.…”

“…A promising strategy for identifying the dark-matter particle is to search for a signature produced by DM decay or annihilation, inside the Galactic halo or at cosmological distances. Although such a signature has not yet been identified, the observed radiation backgrounds have served to constrain various decay and annihilation channels [1][2][3][4][5][6][7][8][9][10][11][12][13]. In many cases, this has resulted in stringent limits on specific DM candidates.…”

Indirect searches of dark matter

“…In contrast to these modeldependent results, in Ref. [6,7], we propose a general method to calculate the signals resulting from electrons and positrons produced in dark matter decays and obtain the relevant constraints from astrophysical observations. Based on the fact that the propagation equation is linear with respect to the electron density, the injected electron energy thus evolves independently.…”

“…Ref. [6,7] point out that the largest uncertainties of the response functions at injection energys above 100GeV come from the poor knowledge about the height of the diffusion zone. The corresponding uncertainties can reach one order of magnitude.…”