Positron Propagation and Fluxes from Neutralino Annihilation in the Halo

TL;DR

This work investigates whether neutralino annihilation in the Milky Way halo can produce observable positron fluxes at Earth. It employs a diffusion-loss propagation model with a Green's-function solution in a slab diffusion zone to compute both continuum and monochromatic positron spectra across an extensive MSSM parameter space, incorporating accelerator constraints and relic-density calculations including coannihilation. The authors find that, under a canonical isothermal halo and standard propagation parameters, the predicted fluxes are typically below detectability, but large uncertainties in halo structure and propagation allow for some models to yield observable signatures and spectral features. They also explore the spectral shapes, including potential line-like features hinted at by HEAT data, and discuss implications for future detectors such as AMS.

Abstract

Supersymmetric neutralinos are one of the most promising candidates for the dark matter in the Universe. If they exist, they should make up some fraction of the Milky Way halo. We investigate the fluxes of positrons expected at the Earth from neutralino annihilation in the halo. Positron propagation is treated in a diffusion model including energy loss. The positron source function includes contributions from both continuum and monochromatic positrons. We find that, for a "canonical" halo model and propagation parameters, the fluxes are generally too low to be visible. Given the large uncertainties in both propagation and halo structure, it is however possible to obtain observable fluxes. We also investigate the shapes of the positron spectra, including fits to a feature indicated by the results of the HEAT experiment.

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