Dark photon production via $$\gamma \gamma \rightarrow \gamma A'$$

Photon Structure and Gamma-gamma Physics

The LEP experiments are making real progress in understanding the structure of the photon, though the results do not yet give such clear demonstrations of QCD in action as the proton structure has done. Other new results are reported, including QED related effects and γγ → Resonances, from LEP and from CLEO II.

Gamma - Gamma , Gamma - Electron Colliders ∗

It is very likely that in 3-4 years the construction of one or two linear colliders with c.m.s energy up to 0.5–1.5 TeV will be started. Besides eecollisions, linear colliders give a unique possibility to study γγ and γe interactions at energies and luminosities comparable to those in ee collisions. High energy photons for γγ and γe collisions can be obtained using laser backscattering. These t...

Gamma Rays from Dark Matter

I give a brief review of high energy gamma-ray signatures of dark matter. The decay of massiveX-particles and subsequent hadronization have been suggested as the origin of the highest energy cosmic rays. Propagation over cosmological distances to Earth (as would be the case in some topological defect origin models for the Xparticles) results in potentially observable gamma-ray fluxes at GeV ene...

Approximation for the gamma function via the tri-gamma function

In this paper, we present a new sharp approximation for the gamma function via the tri-gamma function. This approximation is fast in comparison with the recently discovered asymptotic series. We also establish the inequalities related to this approximation. Finally, some numerical computations are provided for demonstrating the superiority of our approximation.

Gamma - Gamma Colliders