We study three basic diffusion-controlled reaction processes—annihilation, coalescence, and aggregation. We examine the evolution starting with the most natural inhomogeneous initial configuration where a half-line is uniformly filled by particles, while the complementary half-line is empty. We show that the total number of particles that infiltrate the initially empty half-line is finite and h...

In the literature on positron annihilation lifetime spectroscopy (PALS) numerous papers are devoted to the temperature dependence of annihilation parameters: lifetime and relative intensity of various modes of decay. The number of studies on pressure dependence of the same parameters is in great contrast to the previously mentioned: the number is very low. The pressure studies certainly deserve...

Dark matter annihilation in dwarf spheroidal (dSph) galaxies near the Milky Way has potential to produce a detectable signature gamma-rays. The amplitude of this signal depends on dark density dSph, particle mass, number photons produced an annihilation, and possibly velocity-dependent cross section. We argue that if from multiple dSphs can be measured, it is possible determine velocity-depende...

In this article‎, ‎a new scheme inspired from collocation method is‎ ‎presented for numerical solution of stiff initial-value problems and Fredholm integral equations of the first kind based on the derivatives of residual function‎. ‎Then‎, ‎the error analysis‎ ‎of this method is investigated by presenting an error bound‎. ‎Numerical comparisons indicate that the‎ ‎presented method yields accur...

The maximum and the equilibrium numbers of vortex lines are measured in a rotating cylindrical container as a function of its rotation velocity X. We find that a slow cool-down through the superfluid transition at constant rotation produces a state with the equilibrium number of lines, N %2 (X). In decelerating rotation, when vortex lines annihilate, the state is obtained which includes the max...

Gamma-ray positron annihilation spectra of the noble gases are simulated using computational chemistry tools for the bound electron wavefunctions and plane-wave approximation for the low-energy positron. The present annihilation line shapes, i.e. the full width at half maximum, ε, of the γ -ray annihilation spectra for He and Ar (valence) agree well with available independent atomic calculation...

We investigate the temporal evolution and spatial propagation of branching annihilating random walks in one dimension. Depending on the branching and annihilation rates, a few-particle initial state can evolve to a propagating finite density wave, or extinction may occur, in which the number of particles vanishes in the long-time limit. The number parity conserving case where 2-offspring are pr...

We study the production of J/ψ + cc̄ in ee annihilation through two virtual photons. The cross section is estimated to be 23 fb at √ s = 10.6 GeV, which is smaller by a factor of six than the calculated cross section for the same process but through one virtual photon. As a result, while the annihilation into two photons may be important for certain exclusive production processes, the big gap be...

We study the effects of dark matter annihilation during and after the cosmic recombination epoch on the cosmic microwave background anisotropy, taking into account the detailed energy deposition of the annihilation products. It is found that a fairly stringent constraint on the annihilation cross section is imposed for TeV scale dark matter masses from WMAP observations.