Positron annihilation spectroscopy, when combined with highquality supporting modeling of positron states and annihilation in matter, is a powerful tool for detailed defect identification of vacancy-type defects in semiconductors and oxides. Here we demonstrate that the Doppler broadening of the positron annihilation radiation is a very sensitive means for observing the oxygen environment aroun...

We study transition rates and cross sections from first principles in a spatially flat radiation dominated cosmology. consider model of scalar particles to scattering heavy particle production pair annihilation, drawing more general conclusions. The S-matrix formulation is ill suited these ubiquitous processes rapidly expanding introduce physically motivated adiabatic expansion that relies on w...

We theoretically demonstrate a strong dependence of the annihilation rate between (singlet) excitons on the sign of dipole-dipole couplings between molecules. For molecular H-aggregates, where this sign is positive, the phase relation of the delocalized two-exciton wave functions causes a destructive interference in the annihilation probability. For J-aggregates, where this sign is negative, th...

The rate of annihilation of low-energy positrons in many molecular gases is orders of magnitude larger than can be explained on the basis of simple collisions. Developments in positron beam technology have enabled the first energy-resolved measurements of this annihilation process. The results of these experiments provide direct evidence that the large observed values of annihilation rate are d...

We present a geometric interpretation of the so-called annihilation range in reactions of the type p̄p → two light mesons based upon Lorentz effects in the highly relativistic final states (γ = Ecm/2mc ≃ 6.8 − 8.0). Lorentz-boosted meson wave functions, within the framework of the constituent quark model, result in a richer angular dependence of the annihilation amplitudes and thus in higher par...

Observations of annihilation radiation in the Galaxy are briefly reviewed. We summarize astrophysical mechanisms leading to positron production and recent estimates for production rates from nova and su-pernova nucleosynthesis in the Galaxy. The physical processes involved in the production of annihilation radiation in the interstellar medium are described. These include positron thermalization...

There has been considerable recent interest in understanding the kinetics of simple reaction models. Thus far, there are relatively few theoretical methods available to study these reactions and these approaches are usually limited to specific situations. Typically, the transport mechanism of the reactants is specified and the particles interact upon contact. Hence, the use of the representatio...