We know that when an electron, a matter particle, collides with positron, antimatter they annihilate each other as the energy in two particles is carried away by real photons to conserve energy. The same phenomenon occurs all annihilates equal quantity of antimatter. In case charged like proton and antiproton, their opposite charges cancel while neutral neutron antineutron, spins cancel. cases,...

We argue that WIMP dark matter can annihilate via long-lived “WIMPonium” bound states in reasonable particle physics models of dark matter (DM). WIMPonium bound states can occur at or near threshold leading to substantial enhancements in the DM annihilation rate, closely related to the Sommerfeld effect. Large “boost factor” amplifications in the annihilation rate can thus occur without large d...

Energetic positrons propagating along low index directions in a crystal interact strongly with the periodic array of atoms via a process known as channeling. The trajectories of such channeled positrons can be manipulated to sample di€erent spatial regions in the crystal. Here we report the ®rst observations of channeling e€ects on in̄ight annihilation radiation from positrons traversing a thin ...

By solving the Fokker-Planck equation directly we examine the effects of annihilation, particle escape and injection on the form of a steady-state positron distribution in thermal hydrogen plasmas with kT < mec. The positron fraction considered is small enough, so it does not affect the electron distribution which remains Maxwellian. We show that the escape of positrons in the form of electron-...

In a large region of the supersymmetry parameter space, the annihilation cross section for neutralino dark matter is strongly dependent on the relative velocity of the incoming particles. We explore the consequences of this velocity dependence in the context of indirect detection of dark matter from the galactic center. We find that the increase in the annihilation cross section at high velocit...

We calculate the cross section for s-wave neutralino annihilation to three-body final states below the WW and tt̄ thresholds. Such three-body channels may dominate the annihilation cross section if the neutralino mass is not too much less than mt and mW respectively. Furthermore, because neutrinos produced in these channels are much more energetic than those from the bb̄ or ττ channels, they can ...