Ultra-high energy neutrino-nucleon scattering and gluon saturation

Ultra-high energy neutrinos are an enigma; among their many poorly understood aspects are their origins and how they interact with nucleons when they reach the Earth. Due to the hard scale (Q similar to M-W,M-Z) involved in neutrino-nucleon scattering and for a large range of neutrino energies, it is appropriate to describe the target nucleon in terms of its partons - quarks and gluons - and their evolution with Q(2) as governed by the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations of perturbative Quantum ChromoDynamics (pQCD). Nevertheless, at the highest neutrino energies, the scattering cross-section is dominated by the contribution of small x gluons of the target where one expects DGLAP evolution equations to break down due to high gluon density effects (gluon saturation). Here, we give a brief overview of gluon saturation physics in QCD and its effects on ultra-high energy neutrino-nucleon (nucleus) scattering cross-section.