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We consider small--angle electron--positron scattering in Quantum Electrodynamics. Leading logarithmic contributions to the cross--section are explicitly calculated to three loop. Next--to--leading terms are exactly computed to two loop. All the radiative corrections due to photons as well as pair production are taken into account. The impact of newly evaluated next-to-leading and higher order leading corrections is discussed and numerical results are explicitly given. The results obtained are generally valid for high and low energy $e^+e^-$ colliders. At LEP and SLC these results can be used to reduce the uncertainty on the cross--section below the per mille level. PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f
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We present the calculation of the elastic and inelastic high--energy small--angle electron--positron scattering with a {it per mille} accuracy. PACS numbers 12.15.Lk, 12.20.--m, 12.20.Ds, 13.40.--f
We study the single-spin asymmetry, $A_N(t)$, arising from Coulomb-nuclear interference (CNI) at small 4-momentum transfer squared, $-t=q^2$, aiming at explanation of the recent data from the PHENIX experiment at RHIC on polarized proton-nucleus scattering, exposing a nontrivial $t$-dependence of $A_N$. We found that the failure of previous theoretical attempts to explain these data, was due to lack of absorptive corrections in the Coulomb amplitude of $pA$ elastic scattering. Our prominent observation is that the main contribution to $A_N(t)$ comes from interference of the amplitudes of ultra-peripheral and central collisions.
We have derived the coefficients of the highest three 1/x-enhanced small-x logarithms of all timelike splitting functions and the coefficient functions for the transverse fragmentation function in one-particle inclusive e^+e^- annihilation at (in principle) all orders in massless perturbative QCD. For the longitudinal fragmentation function we present the respective two highest contributions. These results have been obtained from KLN-related decompositions of the unfactorized fragmentation functions in dimensional regularization and their structure imposed by the mass-factorization theorem. The resummation is found to completely remove the huge small-x spikes present in the fixed-order results for all quantities above, allowing for stable results down to very small values of the momentum fraction and scaling variable x. Our calculations can be extended to (at least) the corresponding as^n ln^(2n-l) x contributions to the above quantities and their counterparts in deep-inelastic scattering.
Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.
A method to determine the running of alpha from a measurement of small-angle Bhabha scattering is proposed and worked out. The method is suited to high statistics experiments at e+e- colliders, which are equipped with luminometers in the appropriate angular region. A new simulation code predicting small-angle Bhabha scattering is also presented
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