Perturbative quantum chromodynamics

Strong interaction processes, characterised by a large kinematic scale, are described in perturbative QCD by a fixed-order expansion of the partonic cross section in αs. In processes where the centre-of-mass energy s is much larger than the typical momentum transfer t, the sub-process which features gluon exchange in the crossed channel tends to dominate over the other sub-process. That sub-process constitutes the leading-order term of the BFKL equation. (R.P.)