Roman V. Buniy — Page 3

arXiv2002

Electromagnetic Form Factors and the Localization of Quark Orbital Angular Momentum in the Proton

A new picture is given of generalized parton distributions probed in experiments in which the probe scale $Q^{2}$ and the momentum transfer $\DD^{2}$ are well separated. Application of this picture to the $Q^{2}$ dependence of the form factors $F_{1}, F_{2}$ shows that gauge invariant quark orbital angular momentum can be measured and indeed {\it localized} in the transverse profile of the proton. A previous prediction that $\sqrt{Q^{2}}F_{2}(Q^{2})/F_{1}(Q^{2}) \sim const. $ is generalized to GPD language. This prediction appears to have been confirmed by recent CEBAF data.

hep-ph↗

arXiv2000

Radio Detection of High Energy Particles: Coherence Versus Multiple Scales

Radio Cherenkov emission underlines detection of high energy particles via a signal growing like the particle-energy-squared. Cosmic ray-induced electromagnetic showers are a primary application. While many studies have treated the phenomenon approximately, none have attempted to incorporate all the physical scales involved in problems with time- or spatially- evolving charges. We find it is possible to decompose the calculated fields into the product of a form factor, characterizing a moving charge distribution, multiplying a general integral which depends on the charge evolution. In circumstances of interest for cosmic ray physics, the resulting expressions can be evaluated explicitely in terms of a few parameters obtainable from shower codes. The classic issues of Frauhofer and Fresnel zones play a crucial role in the coherence.

astro-ph↗