The cosmic ray positron excess and neutralino dark matter
Edward A. Baltz, Joakim Edsjo, Katherine Freese, Paolo Gondolo
TL;DR
This work evaluates whether the HEAT cosmic ray positron excess can be attributed to neutralino dark matter annihilation within the MSSM, requiring a substantial halo-clump-induced boost factor $B_s$ to enhance the signal. Using a diffusion-loss framework for positron propagation, the authors fit twelve HEAT measurements with a background normalization $N$ and a signal boost $B_s$, while enforcing antiproton constraints via a parameter $k$; they find that $B_s$ must typically exceed about 30 to achieve acceptable fits. A broad MSSM parameter scan shows viable models with $B_s$ in the tens-to-thousands range, including both gaugino- and Higgsino-dominated scenarios, with relic densities $\Omega_\chi h^2$ in an observationally relevant window and possible sizable SUSY contributions to $a_\mu$. Antiproton data (e.g., from BESS) and LEP constraints further shape the viable region, implying that a clumpy halo is essential for explaining the positron excess via neutralino annihilation and guiding expectations for complementary direct and indirect searches.
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 study the dependence on various parameters. We find models with a boost factor greater than 30. Such an enhancement in the signal could arise if we live in a clumpy halo. We discuss what part of supersymmetric parameter space is favored (in that it gives the largest positron signal), and the consequences for other direct and indirect searches of supersymmetric dark matter.