A simple and well-motivated explanation for the origin of dark matter is that it consists of thermal relic particles that get their mass entirely through electroweak symmetry breaking. Furthermore, this possibility suggests an environmental explanation of the hierarchy between the weak and Planck scales and of the small value of the cosmological constant relative to the weak scale. In simple models with these features, the dark matter is a mixture of two Dirac neutrinos with opposite isospin, and so has suppressed coupling to the $Z$. Other minimal models of this form are also consistent with gauge coupling unification. We predict a dark matter (DM) mass of $m_{\mathrm{DM}}\approx 45\mathrm{GeV}$ or $m_{\mathrm{DM}}\approx 90–95\mathrm{GeV}$ and DM-neutron spin-independent cross sections ${\sigma }_{\mathrm{DM}\mathrm{\text{−}}n}\sim {10}^{-6}–{10}^{-8}\mathrm{pb}$. An enhancement of the galactic halo gamma ray and positron flux coming from annihilations of these particles is also expected across the $\sim 1–100\mathrm{GeV}$ range.

• Received 19 August 2005

DOI:https://doi.org/10.1103/PhysRevD.72.093005