Rapidity-Separation Dependence and the Large Next-to-Leading Corrections to the BFKL Equation

Recent concerns about the very large next-to-leading logarithmic (NLL) corrections to the BFKL equation are addressed by the introduction of a physical rapidity-separation parameter ∆. At the leading logarithm (LL) this parameter enforces the constraint that successive emitted gluons have a minimum separation in rapidity, yi+1− yi > ∆. The most significant effect is to reduce the BFKL Pomeron intercept from the standard result as ∆ is increased from 0 (standard BFKL). At NLL this ∆-dependence is compensated by a modification of the BFKL kernel, such that the total dependence on ∆ is formally next-to-next-to-leading logarithmic. In this formulation, as long as ∆ >∼ 2.2 (for αs = 0.15): (i) the NLL BFKL pomeron intercept is stable with respect to variations of ∆, and (ii) the NLL correction is small compared to the LL result. Implications for the applicability of the BFKL resummation to phenomenology are considered.