A modified BFKL equation with Q dependence

Abstract

We propose a modified Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation for the summation of large ln(1/x), x being the Bjorken variable, which contains an extra dependence on the momentum transfer Q compared to the conventional BFKL equation. This Q dependence comes from the phase space constraint for soft real gluon emissions in the derivation of the BFKL kernel. The modified equation gives a slower rise of the gluon distribution function with 1/x for smaller Q, such that the predictions for the structure functions F-2,F-L(x, Q(2)) involved in deep inelastic scattering match the HERA data. These results are similar to those obtained from the Ciafaloni-Catani-Fiorani-Marchesini equation, which embodies both the ln Q and 1a(1/x) summations. The reason that the conventional BFKL equation can not be applied to the low Q (soft pomeron dominant) region is given.