Full One-loop Calculation of Neutralino Annihilation into Two Photons

Abstract

For the first time, a full one-loop calculation of the process $χχ\to 2γ$ is performed, where $χ$ is the lightest neutralino in the minimal supersymmetric extension of the Standard Model. This process is of interest for dark matter detection, since it would give a sharp $γ$ ray line with $E_γ=m_χ$. We improve upon and correct published formulas, and give cross sections for supersymmetric models with $χ$ masses between 30 GeV and several TeV. We find a new contribution, previously neglected, which enhances the $2γ$ rate for TeV higgsinos by up to an order of magnitude. As a byproduct, we obtain a new expression for the related process $χχ\to 2 gluons$, which on the other hand is generally smaller than previously calculated. There has been a recent claim that evidence for a 3.5 TeV higgsino annihilating into a $γ$ line may already exist from balloon emulsion and Air Cherenkov Telescope data. We comment on attractive features and problems with this interpretation.