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The positron excess and supersymmetric dark matter

Edward A. Baltz, Joakim Edsjo, Katherine Freese, Paolo Gondolo

TL;DR

This work investigates whether the observed cosmic-ray positron excess reported by HEAT can be explained by neutralino annihilation in the galactic halo within the MSSM framework. Using a diffusion model for positron propagation and a boost factor $B_s$ to account for halo clumpiness, the authors perform a MSSM parameter scan with DarkSUSY, enforcing cosmological and accelerator constraints. They find that fitting the HEAT data generally requires substantial signal enhancement, with $B_s$ ranging from ~30 to as high as $10^{10}$ in extreme cases, and that antiproton flux constraints limit the viable parameter space. The study highlights realistic mass ranges and neutralino compositions that can accommodate the data, while noting the need for halo structure assumptions and potential fine-tuning to explain sharp spectral features.

Abstract

Using a new instrument, the HEAT collaboration has confirmed the excess of cosmic ray positrons that they first detected in 1994. We explore the possibility that this excess is due to the annihilation of neutralino dark matter in the galactic halo. We confirm that neutralino annihilation can produce enough positrons to make up the measured excess only if there is an additional enhancement to the signal. We quantify the `boost factor' that is required in the signal for various models in the Minimal Supersymmetric Standard Model parameter space, and find that a boost factor >30 provides good fits to the HEAT data. Such an enhancement in the signal could arise if we live in a clumpy halo.

The positron excess and supersymmetric dark matter

TL;DR

This work investigates whether the observed cosmic-ray positron excess reported by HEAT can be explained by neutralino annihilation in the galactic halo within the MSSM framework. Using a diffusion model for positron propagation and a boost factor to account for halo clumpiness, the authors perform a MSSM parameter scan with DarkSUSY, enforcing cosmological and accelerator constraints. They find that fitting the HEAT data generally requires substantial signal enhancement, with ranging from ~30 to as high as in extreme cases, and that antiproton flux constraints limit the viable parameter space. The study highlights realistic mass ranges and neutralino compositions that can accommodate the data, while noting the need for halo structure assumptions and potential fine-tuning to explain sharp spectral features.

Abstract

Using a new instrument, the HEAT collaboration has confirmed the excess of cosmic ray positrons that they first detected in 1994. We explore the possibility that this excess is due to the annihilation of neutralino dark matter in the galactic halo. We confirm that neutralino annihilation can produce enough positrons to make up the measured excess only if there is an additional enhancement to the signal. We quantify the `boost factor' that is required in the signal for various models in the Minimal Supersymmetric Standard Model parameter space, and find that a boost factor >30 provides good fits to the HEAT data. Such an enhancement in the signal could arise if we live in a clumpy halo.

Paper Structure

This paper contains 4 sections, 1 figure.

Table of Contents

  1. Introduction
  2. Supersymmetric model
  3. Positron spectra and fits to the HEAT data
  4. Conclusions

Figures (1)

  • Figure 1: Positron fraction data and fits. We illustrate positron data from HEAT 94+95 and HEAT 2000, a background only fit, and a SUSY+background fit for two interesting MSSM models. Two additional curves separately display the SUSY and background components of the combined SUSY+background fit. These models are gaugino dominated and the model in a) has positrons primarily from hadronization, while the model in b) has hard positrons from direct gauge boson decays.