Resonant Scattering and Charm Showers in Ultrahigh-Energy Neutrino Interactions

Electron antineutrinos with energy ∼ 7 × ${10}^6$ GeV have much-enhanced cross sections due to $W$-boson production off electrons. Possible signals due to cosmic-ray sources are estimated. Higher-energy antineutrinos can efficiently produce a $W$ accompanied by radiation. Another possibility, which could lead to shadowing at modest depths, is resonant production of a charged Higgs particle. The importance of muon production by charm showers in rock is pointed out.