γ* - γ* scattering: Saturation and unitarization in the BFKL approach

In this paper γ*-γ* scattering with large, but more or less equal virtualities of two photons is discussed using BFKL dynamics, emphasizing the large impact parameter behavior (b_t) of the dipole-dipole amplitude. It is shown that the non-perturbative contribution is essential to fulfill the unitarity constraints in the region of b_t < 1/2m_π, where m_π is pion mass. The saturation and the unitarization of the dipole-dipole amplitude is considered in the framework of the Glauber-Mueller approach. The main result is that we can satisfy the unitarity constraints introducing the non-perturbative corrections only in initial conditions (Born amplitude).