Duality symmetry of the Balitsky-Fadin-Kuraev-Lipatov equation: Reggeized gluons versus color dipoles

It is shown that the duality symmetry of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation can be interpreted as a symmetry under rotation of the BFKL kernel in the transverse space from s channel (color-dipole model) to t channel (Reggeized gluon formulation). It is argued that the duality symmetry also holds in the nonforward case due to a very special structure of the nonforward BFKL kernel, which can be written as a sum of three forward BFKL kernels. The duality symmetry is established by identifying the dual coordinates with the transverse coordinates of a nondiagonal dipole scattered off the target.