Gamma ray lines from TeV dark matter

Abstract

We calculate, using unitarity, a lower bound on the branching ratio $χχ\to γγ$ and $χχ\to γZ$, where $χ$ is any halo dark matter particle that has $W^+W^-$ as one of the major annihilation modes. Examples of such particles are supersymmetric particles with a dominant Higgsino component, or heavy triplet neutrinos. A substantial branching ratio is found for the $γγ$ and $γZ$ modes. We estimate the strength of the monoenergetic $γ$ ray lines that result from such annihilations in the Galactic or LMC halos. (Latex file; 2 compressed uuencoded postscript figures available by anonymous ftp from vanosf.physto.se in file pub/figures/lines.uu)