Penetration of the Earth by ultrahigh energy neutrinos and the parton distributions inside the nucleon

In this talk we would like to present recent calculations of the cross sections for the ultrahigh energy neutrinos interacting with nucleons. We briefly present the framework of unifed BFKL/DGLAP equations which resums all the leading log(1/x) effects as well as the subleading terms. The few free parameters which specify the input parton distributions are determined by fitting to HERA deep inelastic data. We then use these parton distributions to calculate the cross section for the neutrino-nucleon interactions at very high energies, up to 10^12 GeV. We do also investigate the attenuation of neutrinos when traversing through the Earth. We use the transport equation which we solve for different fluxes of high energy neutrinos (Active Galactic Nucleai, Gamma Ray Bursts, and top-down models). We study the effects of the regeneration of the neutrino flux via neutral current interaction.