Nonlinear $k_{\perp}$-factorization: a new paradigm for an in-nucleus   hard QCD
  We review the origin, and salient features, of the breaking of the conventional linear $k_{\perp}$-factorization for an in-nucleus hard pQCD processes. A realization of the nonlinear $k_{\perp}$-factorization which emerges instead is shown to depend on color properties of the underlying pQCD subprocesses. We discuss the emerging universality classes and extend nonlinear $k_{\perp}$-factorization to AGK unitarity rules for the excitation of the target nucleus. 
N. N. Nikolaev (IKP FZ Juelich and Landau Inst.), W. Sch\"afer (IKP FZ   Juelich), B.G. Zakharov (Landau Inst.) and V.R. Zol...