Low x QCD and Penetration of Ultrahigh Energy Neutrinos Through the Earth

In this talk we present a calculation for the cross sections for neutrino interaction with the nucleon. Parton distributions are calculated using the unified BFKL/DGLAP formalism which embodies also important subleading ln 1/x effects. It is shown that this calculation is consistent with the other based on GRV and CTEQ parton distributions up to 40% for the highest energies: ∼ 1012 GeV. We also calculate the attenuation of neutrinos on their way through the Earth to the detector. We solve the transport equation which also embodies the regeneration due to neutral current interactions besides attenuation. We present the results for different angles and fluxes originating from different sources like active galactic nuclei, gamma ray bursts and top-down models. (author)