B.I.Ermoiaev (Ioffe Phys.Tech.Inst.)


Light-by-light scattering in double-logarithmic approximation


We consider the elastic 2 ! 2 -scattering of virtual photons at high energies in the forward kinematics with zero and non-zero t. We obtain explicit expressions for amplitudes of this process in double-logarithmic ap- proximation (DLA), keeping the QCD coupling first fixed and then running. Then, using the saddle-point method, we calculate the small-x asymptotics of those amplitudes, which proved to be of the Regge form, with the Reggeon bearing the vacuum quantum numbers, i.e. a new Pomeron. We compare our Pomeron to the BFKL Pomeron. Our comparison shows that contribution of our Pomeron to the asymptotics is of the same order as contribution of the BFKL Pomeron. We demonstrate that the value of the intercept decreases with increase of accuracy of the calculations. We also study the applicability region of the Regge asymptotics and estimate the minimal value of s, where the asymptotics can reliably represent the parent amplitudes