The Yin and Yang of high energy chromodynamics: Scattering in black and white Original Research Article

We further discuss the QCD reggeon field theory (RFT) as it emerges from the JIMWLK/KLWMIJ evolution equation and beyond. We give an explicit expression for the calculation of scattering amplitude in terms of the eigenstates of the RFT Hamiltonian. We point out that the spectrum of RFT is doubly degenerate, the degeneracy being related to the spontaneous breaking of the dense–dilute duality symmetry of RFT. The degeneracy is between the “almost white” states (the Yang sector) which contain a small number of gluons, and “almost black” states (the Yin sector). The excitations above the Yang vacuum have natural interpretation in terms of gluons. Analogously the excitations above the Yin vacuum have natural interpretation as “holes” in the black disk—points at which an incoming gluon does not scatter with unit probability. We discuss in detail the spectrum of the “parton model approximation” to the KLWMIJ evolution introduced in our previous paper, and prove that it is explicitly selfdual. This allows us to find explicitly the counterpart hole states in this approximation. We also present an argument to the effect that the end point of the evolution for any physical state cannot be a “grey disk” but must necessarily be the “black disk” Yin vacuum state. Finally, we suggest an approximation scheme for including the pomeron loop contribution to the evolution which requires only the solution of the JIMWLK/KLWMIJ Hamiltonian.