Ultra-high energy neutrino-nucleon scattering and gluon saturation

Abstract

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 ([Formula: see text]) 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 [Formula: see text] 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 [Formula: see text] 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.