We calculate the amplitude of elastic photon-photon scattering via a single quark loop in the Double-Logarithmic Approximation, presuming all external photons to be off-shell and unpolarized.. At the same time we account for the running coupling effects. We consider this process in the forward kinematics at arbitrary relations between t and the external photon virtualities.
We obtain explicit expressions for the photon-photon scattering amplitudes in all double-logarithmic kinematic regions. Then we calculate the small-x asymptotics of the obtained amplitudes and compare them with the parent amplitudes, thereby fixing the applicability regions of the asymptorics, i.e. fixing the applicability region for the non-vacuum Reggeons.
We find that these Reggeons should be used at x < 10^{-8} only.
I derive an all-order resummation formula for the logarithmically enhanced contributions proportional to $\frac{α_s^n}{x \pm ξ} \log (\frac{ξ\pm x}{2ξ})^k$ in the quark coefficient function of deeply-virtual-Compton scattering and the pion-photon transition form factor in momentum space. The resummation is performed at the next-to-next-to-leading logarithmic accuracy. The key observation is that the quark coefficient function itself factorizes in the $x \rightarrow \pm ξ$ limit, which allows for a resummation using renormalization group equations. A preliminary numerical analysis suggests that…
We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer $ Q^2 $. We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the $ Q^2 $ expansion of the TPE correction and goes beyond this approximation by keeping the full $ Q^2 $ dependence of the proton …
We present the current status of the Next-to-Next-to-Leading Order QED contribution to the $μe$-scattering. Particular focus is given to the techniques involved to tackle the virtual amplitude and their automatic implementation. Renormalization of the amplitude will be also discuss in details.
Department of Physics and Astronomy, University of Sussex(萨塞克斯大学物理与天文系);Dipartimento di Fisica, Università di Genova and INFN, Sezione di Genova(热那亚大学物理系和意大利国家核物理研究所热那亚分部)