Gluon-gluon elastic scattering amplitude in classical color field of   colliding protons
  We present a formalism for gluon-gluon elastic scattering in the presence of the classical color field of the protons in high energy collision. The classical field is obtained by solving the classical Yang-Mills equation in the covariant gauge and treated as a prescribed background for the quantum gluons involved in the scattering process. The interaction between the classical field and the quantum gluon modifies the gluon propagator, and, in turn, the $gg\rightarrow gg$ amplitude. The modified gluon propagator is derived to the first non-zero order of the classical field using the Gaussian approximation in Color Glass Condensate and shown to satisfy the generalized Slavnov-Taylor identity. This formalism is the theoretical basis for our recently proposed classical color field modified minijet model where we show that the $pp$ and $\pbar p$ cross section data from $\sqrt{s}=5$ GeV to 30 TeV can be satisfactorily fitted and the model predicts a $(\ln s)^2$ behavior for large $s$, which saturates the asymptotic behaviour of Froissart bound. 
Man-Fung Cheung and Charles B. Chiu
hep-ph nucl-th